I'm really hankering to thread a Good Omens slash line between Crowley/Aziraphale (I'd play either), preferably something that has a mix of dark and light (even comedic) moments. I've got a vague premise that involves them one day waking up human for reasons unknown, and they have to adapt to mortality and their new human needs together. Crowley can continue to inflict a little corruption on Aziraphale, who in turn will continue to prove that the demon isn't really all bad.
It'd be epic to have a plot of some sort going on for them to develop through. Like, they decide that something must be wrong Above or Below, so they go on another adventure to find out what's happening, escaping a few interesting people, leaving a trail of destruction along the way, even get discovered by someone realising the angel and demon are mortal and try to catch them. Maybe Adam the Antichrist has become a teenager, and with hormones and desires raging through him, he's caused a major divine disruption (and created disorder on a more Earthy level, such as freak weather, kamikaze ducks, and wandering hordes of Casanovas prancing across Britain, etc.) and the pair have to figure out a lot more about relationships for themselves before they can start to help the moody Antichrist. Or, y'know, something completely different.
I'm not picky about PBs, although if we can each offer a bunch of suggestions of who we'd play or like to play against, that would be all levels of fabulous.