I liked the early UU stuff. Still mighty big fan of USM, but I liked the first few volumes of UXM, and the first UFF. I adore the hell out of Ultimate Daredevil and Elektra and the fact that the Daredevil in USM is nowhere like the one in UD&E made me sad.
I think the concept could work if they adhere to the shared sandbox that characterized the early Ultimate Universe. Y'know, the fun stuff. Like the Ultimate Annuals. Man, did they wreck each other's continuity, but it was fun. Maybe a more All-Star sort of take? I think especially the Fantastic Four lend themselves to this very well. FF is MADE for wacky sci-fi. You'd think they could get beyond just Galactus and whatnot and seriously make some serious Kirby-esque mania.