I've thought about this a few times before and the consensus I typically reached was that people wouldn't show up to app, lol. I think what could work better is a sort of open musebox/dressing room that allowed AUs and OCs. I think AUs would fit more seamlessly into the setting and having OUs just being revived there would introduce a running theme where everyone wants to leave and I'd rather have a game that has basically the opposite (OTOH, the image of a bunch of OU characters joining Dead Orbit is kind of funny, Jalaal would be so pleased).

Honestly I think a Destiny game would have taken off if it managed to get in before the big space/sci-fi wave that swept DWRP last year, but alas.