I know people on here are big fans of Fantastic Four and X-Men, but I'm not convinced they're the easy cheat codes to success that they seem to be discussed as. Especially Fantastic Four. Movie seems interesting so far, it'll make money, but I'm not convinced on the modern pop cultural penetration of those characters at the moment. X-Men, better chances, but I think the difference between something like the Avengers and that is that X-Men are... well, the X-Men. It's an arm of the universe that can operate pretty much independently and, as a result, bringing in disparate characters seems likely to feel like guest starring even in a big scale event. Not sure it could serve as a spine in the same sense that Avengers has previously. But it all just depends on how people respond. It'd be premature to discontinue the Avengers brand (and its hibernation I'd point to as a key reason Marvel's been struggling as of late, imo) before seeing if people react positively.