There is another possibility:
Drop-in, drop-out co-op where there is the MC but also a bunch the ability to control the other members of the party online. This could be a bit easier to work in with the main story. Of course, since this will work like Xenoblade almost certainly in that everyone follows you but only x number are in your party so it's not like you can "lose" plot central characters.
If it is standard online co-op, I wonder how you meet up? Maybe you can uplink at the various "vantage points" seen on the gamepad in the Direct? Or maybe the military outposts or BLADE Tower? And I wonder if any of the non-MC characters will appear in the cutscenes?
PS: now I know why the quality of the soundtrack kept bouncing around all over the place xD . Great to here the site got a lot of hits!
PPS: aaaaaand there's the first downer. That didn't take long :P
