My definition of what is (or isn't) a "big bang" theme is simple - is there a cartoon series to accompany it? If there is, then it's a "big bang" theme; if there isn't, it isn't. Simple :-)
As for the next non-ip/non-"big bang" theme, I'd love to see a return to Classic Space, particularly something with a back story around exploration and adventure. Unfortunately, if we do get a new Space theme, it's not going to happen quite like that. Lego's current philosophy of encouraging conflict-based roleplay wouldn't allow it; they feel the need to always provide "good guys" & "bad guys", in conflict with each other. But, as long as there are spaceships involved, I'll be happy.