First of all, Iron Man wants no part of the 'evil X-Men'. That's fucking scary. It would take like two of them to kill him... like any two. Besides if our 50+ X-Men did turn evil, there really wouldn't be anything stopping them from taking over the world. The Fantastic Four? Please. Reed can't even notice his wife's boobs let alone a mutant ambush. Fucking Reed. Anyway...
The plague idea pretty much peaked with zombies. There really isn't anything else people could get turned into besides zombies that would make it fun. Maybe fake mutants? But honestly, I could play zombies again. Unfortunately, I think I'm in the minority there.
As far as a terminator plot, I kind of like that. Especially because in every form 'the sentinels' end up becoming self-aware. So I think that would probably happen no matter what. I don't know if it would go as far as you stated, because I don't think the girls (Becky, Leigh and Jordan) are as interested in playing a 'post-apocalyptic' style game right now. Because if they did, we'd probably have zombies, lol.
Right now, I think we should focus on the fact the game is changing a lot. It's pretty much closed to everyone but us five, and we're trying to branch out into new locations. I think we were all sick of every thread taking place at the Mansion. On the new taken page people are already divided into five different locations (the HFC isn't so much a location but characters listed there are going to be spending less time at Xavier's). Plus, we've got a bunch of new characters (Teen X-Men, Iron Man, FF, maybe Spidey) that need to get played. And 'X' is still out there, which is a pretty scary thing.
While I think we need to have our eyes on the future (ie; some big world changing plot) I think right now everything should probably be much smaller and character driven. We are all alone on this island. We can spend as much time on developing people and less time on 'big Hollywood plots' to bring in new players. If we just spent some time playing all the characters I think plot would create itself. I feel like I barely know my characters, not to mention all the others.