Catch Trap
I can also see a story written from Angelo’s perspective, of how he sees Tommy/Mario or even Tommy/Bart or how he saw Mario/Bart when Mario was a teenager. Character wise, I don’t like to see Angelo as a demon, he is a man of his time and his homophobic behavior really is a consequence from that.
In the friendship front, I would love too see Mario and Angelo when Matt was a kid or when Matt was a teenager and he first meet Bart.
Bronte
I think mostly this fandom is a gen/friendship thing, so I not talking much about it.
Teahouse
Linneus is that good guy, sweet beyond measure, so I see him having a awesome friendship with Rory, teaching him things or just being there when he fills traped or need comfort.
You can also make a Linneus centric fic or a Rory centric fic, with them talking about their lives in Teahouse: the daily life, the other characters and how they manage them, abou their clients or even what are their preferences in bed or to eat. I love character studies and how they can work in building a biography to that character you don’t have much to think about.
Darkover series
This is the story where I don’t have many preferences, I mostly would like to see Danilo and Regis having fun together, training, or just having a field trip. I love when they have all those telepathic conversations.