I've read that Misha Collins will be a series regular on SPN if it gets a fifth season (which is looking more and more likely as I cross my fingers). (ETA: Article:
here.) While I probably like Misha Collins more than the average fan (I do mod
mishaland after all), I am not sure I like this. Jim Beaver isn't a series regular. JDM wasn't a series regular. I don't think either Ruby was a series regular. While I do like Castiel as a character and think he provides a good counterbalance to the demons, especially Ruby, this is a show about two brothers.
Misha is awesome. I love him dearly. I kind of want to grow up to be him. I am already from Massachusetts and have an improbably ethnic name.
I love Castiel. I have a thing for angels who question authority. I think it comes from growing up Catholic. They can't feel guilt so we can push all of our guilty Catholic needs onto them. I like that Castiel can kick ass and take names (4.01 Lazarus Rising) and then have moments of softness (4.07 It's the Great Pumpkin, Sam Winchester). I like that he's trying to learn to be human and that he still loves God and that he trying to learn compassion and seems to have a better heart than Uriel.
However, he still isn't Sam and Dean. I still think that season two was the best season ever and love to read and write fic there. The show is "epic love story of Sam and Dean," not the show about two guys and their angel buddy.
The one thing that could make this sit better with me is if Ruby became a regular, too. I don't much like Ruby for reasons I have trouble articulating, but Castiel makes me like Ruby more (and I think I might like Castiel more because of Ruby).
Castiel feels like an important counterbalance to Ruby to me. This means that if Castiel became more important, then Ruby would need to counterbalance him for me. They come from opposite sides (Heaven and Hell) and are both trying to move toward the middle (Earth, humanity). I think they could learn a lot from each other if they stopped hating each other so much. They are very much the same.
However, were Castiel alone (or Ruby alone or Bobby alone) to become a regular like Sam and Dean, I would be a sad panda. I'm not even sure why I feel like it would ruin the balance and dynamic of the show, but I think it would. As much as I love our resident angel, he is nowhere near as important as Sam and Dean.