This wasn't one of those things that particularly clever people were able to suss out from reading a few different solicitations together and making an intuitive leap--rather, it comes from a quick look at the solicitation text for Cataclysm #2. The previously-announced event that sees the "616 Universe" version of Galactus head to the Ultimate Universe hungry for an Earth-shaped snack is now officially retitled ominously as Cataclysm: The Ultimates Last Stand. And, yes, the solicitation confirms without question that the Marvel Universe will meet Miles:
CATACLYSM: THE ULTIMATES LAST STAND #2 (of 5) BRIAN MICHAEL BENDIS (W) • MARK BAGLEY (A) Cover by MARK BAGLEY Variant Cover by TBA • The ULTIMATES discover where GALACTUS has come from • If they send the WORLD DESTROYER back to where he came from all that will do is create more destruction and havoc! • MILES MORALES is headed to the Marvel Universe 32 PGS./Rated T+ …$3.99
...So there's that. The announcement of a new character appearing in Mighty Avengers by the name of Spider-Hero is an interesting addition to the roster, given the timing, and seems likely to be Miles's name--at least temporarily. It doesn't sound like the kind of name you can hold onto long-term.