It feels like Rosenberg is on Uncanny for the long haul, so it would be weird to see him suddenly jump of it, and given they probably knew he was gonna be coming back since before Disassembled started, it seems even weirder he'd be on it for so short and supposedly have much more still to do. If it is an X-book, it probably is gonna be a new one with a new team that spins directly out of the end of Age Of X-Man.
But either way, I'm really excited for it, Hickman is excellent, and I love that all they have to do is put his name on a white sheet of paper and people go crazy. Just like all the "Bendis is Coming" teasers from DC books last year, sometimes all you need is a name to draw hype!