You Say Interactive Fan Fiction Like It's A Bad Thing
I've not modded a game for a good long while, not since I used to play around with UT for research purposes (honest!). Having dipped my toe slightly into the DAO modding world thanks to going to find the 'Equal Love' mod (*pets Alister*) I had a look around at some of the other things that were going on. There are a few interesting looking mods (or possibly will be if they get finished) - for example, Bond of Blood for example 'explores' the relationship between the two Wardens although there is a definite hint of this isn't slash because what we are doing is good and deep and meaningful and has plot and something or other (which irritated me a little and since they seem to be going for the 'not gay it's just your character because of the deep bond due to the joining' I really am not sure they have much of a leg to stand on without getting into a bunch of gender/sexuality meta which I am not about to touch with a very long lance anyway...).
Now, I'm not sure exactly what it was about running around the landscape putting ghosts, demons and monsters to rest, occasionally dealing/using magic and dealing with the deep parent/abandonment issues of one of my party members made me think of a particular show but somehow it did. Admittedly all the female characters in DAO aren't dying horribly, and there are quite a few who are both powerful and alive and not evil.
You know how these are - you try not to think about it but things just bubble around in your mind.
Is There Pie?
So the basic story would allow you to play either Dean or Sam and you would get the other as an initial party member. Unlike DAO you would have a max party size of three which would allow you to take one other person from those recruited with you on missions. Other possible party members would include:
Bobby
Jo
Castiel
Anne
Ruby
Critters/demons (see below)
Witch/wizard/psychic
The models that come with the game are surprisingly configurable facially and there are lots of mods for expanding the hair/skin/tattoo coming out so it probably wouldn't be too difficult to create something approximating the necessary visuals.
Necessary locations would be Bobby's place, Jo's bar and then a bunch of buildings and graveyards for them to general wander around in the search for pie, hauntings, monsters and other gribblies. And possibly trying to stop the Apocalypse and defeat Lucifer on the side. The cars might be a bit of a problem but otherwise there are lots of models for buildings and terrain and graves in the game. Not sure how easy that it to tinker with but some of the mods coming out have new territory so it is clearly doable.
It would be necessary to tweak the races, skills and spells options. The three main races we would need are human (magic user, hunter, normal), angel (archangel, normal, rebel, fallen) and demon (damned, demon, lord).
Demon magic would tend towards the nasty similar to the current entropy and blood magic spells, Angels could get a combination of healing, Templer and primal smite-y spells, humans would be limited to things like glyphs and anti-magic unless they could get a power boost somehow - for example through a deal with an angel or a demon which would open up some of the respective spell options. Humans could have a 'ritual' track as well for things like exorcisms. For Angels, grace would replace mana while for human magic users and demons it would be psychic energy.
As far as skill sets go - coercion, stealing, survival, herbalism, poisons, combat skills and combat training could probably transfer as is. You would have to mess around with what you could make with herbalism and poisons (maybe name them slightly differently) but they could allow characters to make things like holy water, hex bags, rock salt bombs etc. I'd be tempted to replace trap skills with electronics just to update things a bit - it would allow you to set up and disable security systems. I'd love to have driving but I think that would just complicate matters and I note the game doesn't have riding either, probably for similar reasons. Maybe you could just have the Impala appear in the group campsite and the trunk acts as a group equipment stash. It would probably be worth lowering the number of equipment slots that the party had - partly to represent that less party members == less carrying space (riiiight!) but mostly because I think there would be less types of useful items (runes, rock salt, petrol, fire lighter, guns, ammo, phosphorus ammo, salt ammo, holy water, money etc) and therefore less slots needed to keep the same 'can-i-carry-everything' tension.
Talents would require a bit more tweaking. But basic areas could be something like research (languages, hacking...), hustling (lock-picking...), combat (melee, missile...) etc
Hacking is a little problematic because it would necessitate having something you could use it for. One interesting possibility would be to take the DAO fade and turn that into a cyberspace analogy. In that same way that there is a the fade mission, you would have a mission in which the characters have to carry out tasks in cyberspace, possibly having to interact with Winchester Chronicle fans online to find someone/some information. That aside you could have computers which could be hacked in various places (like locked chests) as a source of funds/objects (online ordering).
Things like the Mages collective/Black stone irregulars would be replaced by Hunter networks, reformed vamps/non-homicidal supernatural critters etc.
Gifts could be character appropriate - Dean: car parts, food (and porn ?), Cas: religion items, Sam: books and computer upgrades, Jo: weapons, Bobby: research books etc etc.
Which brings us on to the fun bit - plot and character interaction.
Clearly the basic plot would be a main plot arc of stopping Lucifer/the Apocalypse with the sub plots being the hunting jobs that are need to be taken of in the mean time, the search for clues about how to stop Lucifer and rounding up allies for the big final battle (pretty much the plot of DAO). Random encounters while travelling will be mostly fights to save seals as Angels pop up, ask for help and then then zap you to the seal and back again afterwards if you agree to help. If you don't help then the seal will probably fall and demons and demon magic will get a boost.
And you will gain corruption points. The game already comes with an approval rating slider so that characters can approve or disapprove of the main characters actions. It doesn't really have any concept of good/evilness of the characters beyond what they approve and disapprove of and how the player chooses to behave. The closest is that you can 'harden' (no jokes from the peanut gallery) you characters to make them more self-interested (more willing to be king, have threesomes etc) but that is a on/off toggle. What I think would makes things a lot more interesting would be to have a corruption bar as well as the approval bar. So certain actions (choosing not to save innocents, choosing not to save seals, drinking demon blood, making deals with demons, for example) would give the character corruption points. Become corrupt enough and Angels become fallen Angels and humans become damned and gain demon powers. The more corrupt you are the more powerful demon magic is/can be but on the other end of the scale you can work your way up the scale and gain grace and start possibly getting access to Angel magic. It should be harder to get redemption/grace than it should be to get corruption/lose grace. Most humans will start of around the zero-mark, angels start with high grace and demons with high corruption.
Just to make things more twisted the options that the character get will change depending on their corruption level. So a character with higher grace may get less chance to not save the innocents because they just wouldn't think of that possibility while a character with very high corruption might not get the option to save them unless they could be useful. I think this would work by having a margin of error - within that corruption/grace range then you would just get approval/disapproval for your actions. Outside that range then the amount of approval/disapproval that an action would receive would be altered based on the difference in rating. Not only that but the character with the higher grace rating would gain some corruption if they agreed to go along with the corrupted character and might refuse to help if they didn't. This could result in them leaving the party (if it was bad enough) or just not coming along on that part of the mission. High approval and cunning/coercion means that you are more likely to be able to talk the characters into doing what you want.
NB. Rebel angels are not necessarily fallen although they may become so. However their grace pool for spells maxes out at whatever their grace level is so as they become more corrupted their powers are weakened. Non-Rebel angels are linked to the angel grace network and so regen grace quicker and can't loose it. They also can't join the party so to get an angel in your ranks you have to get a high enough approval rating that you can talk them into defying heaven's orders for you and rebelling. Then when they are in your party you have to worry about how much you are corrupting them. Angels and archangels can't be romanced, rebel angels can, as can fallen angels (although they tend more towards the sex rather than the romance), demons and non-related humans (at least at normal corruption levels).
It would however be a bit silly if there was no way to finish the game if you get too corrupted. So there would need to be an alternative 'dark side' ending where the boys stop Lucifer and the Apocalypse... by Sam killing him and taking his place to reign in Hell. If your main character tips over into 'damned' then either you have corrupted the rest of your party enough that they stick with you or you haven't which will result in them leaving and possibly trying to kill you on the way out. A number of other possible companions will also become available such as demons who wouldn't have considered joining you previously. It that situation, when travelling it won't be angel popping up and asking for help to save the seal it will also be demons popping up and asking for help to break them. Demons are more likely to be friendly with you and angels will attack.
The sub-finale decision will be the possession fight in which either Micheal or Lucifer asks to possess Dean or Sam respectively (depending on corruption levels - if Dean and Sam are both corrupted then Lucifer will approach, otherwise Micheal will approach although if Dean is corrupted he won't ask so it will be a straight fight and even if you are playing as Sam and Dean isn't in the party then you will get a chance to intervene on his side if you choose). If you say yes then the character becomes Micheal or Lucifer and you take them into battle against Micheal + Angels (if Samifer) or Lucifer + Demons (if Deaneal). They sacrifice themselves and the final battle is won or lost. Alternatively, Sam/Dean tells Lucifer/Micheal to get lost and don't take kindly to 'No' as an answer. If it is Micheal wanted to possess Dean then it is a matter of beating him to show that you are strong enough to go up against Lucifer without being possessed. Losing gets you possessed, winning gets you Micheal and the ranks of angels on your side in the final battle. If it is Lucifer then the fight is on for Sam's soul. Losing gets him possessed and the remaining party gets the choice to join Lucifer for the finale battle against the angels or to try and kill Samifer with the angels on your side but not allied. Winning means destroying Lucifer and taking his place as Lord of Hell. You then have to fight Micheal and the massed ranks of angels as they try and take you down.
Edit (post-finale) - With the season finale, the basic plot actually becomes a even more obvious - the side missions are all to get the rings from the horsemen so that Lucifer can be trapped again during the final battle. If Dean says 'Yes' to Micheal then it is a straight up battle between Deaneal and Lucifer/Samifer (depending on whether Sam says yes or not), if Dean says 'No' then the plan is to trap Lucifer/Samifer (depending on whether Sam says yes or not) with the rings for the final battle with possible option for taking on Micheal (or Zak) first. The corruption track would remain pretty much the same with Lucifer needing to be defeated so that Sam/Dean can rule in Hell safely and then optionally fighting the Angels for complete control of Earth (as a benevolent Evil Overlord).
Not that I have thought about this at all. In some ways I am quite glad that I am using a Mac at the moment since that pretty much removes the temptation of having a play with thing (the toolkit appears to be PC only). Hopefully now I have written this all down I can stop turning it over in my head.