I think we best limit ourselves to one big game at a time; it is hard enough to have subs for one big game, let alone have players and subs for two big games that are running concurrently.
Lately, there's been talk about running two Lites simultaneously, and I think it's something we could try. Lite tends to fill up pretty quickly, and if we can get ~35 players for a big game we should have enough for two Lites.
Regarding other games, I don't see why there should be any limit. BSG concerns only a handful of people (and a couple of Cylons!) at a time. People who played Dark Cult back in the days were mostly the same people who played/play Werewolf. I think it's logical that these games are placed here.