I still don't see how the 360 is even capable of doing an MMOFPS.
The PS3 tried to do it with MAG but that failed miserably and the graphics were crappy as all of the seven hells. The 360 really can't support more than about 24 players for an optimized FPS.
The game probably won't feel like an MMO at all if they're shooting for an xbox release. I can guarantee it. Subscriptions? HELL YES. They will do it. They did a -blam!- subscription for HALO 3/ODST/REACH, you can bet your wallet they'll do it again for Destiny. Probably won't be mandatory, though.
IMO, Bungie's last release, Halo Reach, was an atrocity so they're going to have to release a very good game to catch my good side.
Oh and by the way, from what I can tell, this game is probably going to feel a lot like Armored Core V, except with forced factions rather than custom ones. Conquer territories for your faction, etc. MAG did this too.
[Edited on 11.27.2012 7:01 PM PST]