Umm.. they already did just that.

Bungie bought themselves "back" from MS, because they didn't want to do what Ensemble did, and splinter and reform into smaller groups.  If they hadn't done so, they'd be gone now, and Halo ODST and Halo: Reach would probably be internal MS projects, or just plain nonexistant.

As is, they are probably doing the work for cheaper than what MS would have had to pay, 1st party.  Cheaper because MS doesn't want to pay their entire staff...

There is a lot of camaraderie in the longer-standing studios -- they do not like to fire people that don't deserve it, just because they cannot find a publisher to pay the bills for their entire staff, via enough projects.  MS won't pay for the whole staff any longer (this is why they let Bungie go in the first place)... hence Bungie finds a second publisher, because they have the talent to work on more projects than MS is willing to pay for at one time.

I am 99% certain MS is not the publisher of the new project.

More information on this mysterious new IP will be revealed next year. Screen shots, footage, etc could debut at E3 10'

If its Wii, it could explain the difficulty in finding a publisher. I doubt it though.

It should be multi-plat so Sony fans can worship Bungie as well. You can bet there will be closet fans of the game, they've been calling Bungie crap for so long I can't blame them for hiding their deep love for the new IP.

Never ceases to amaze me how people think that MS needs Bungie more than Bungie needs MS. Wasn't it Microsoft's marketing that helped every Bungie Halo game to bust out HUGE? Why would they want to work with a DIFFERENT publisher?

Anyway, a non-MGS published Bungie game will be beloved prematurely by many a fanboy. *sigh*

+1.  Or really, letting Steve Ballmer run the company.  Surely he did some things for the company way back that were critically important.  But right now he's a crappy leader with little to no vision - or a vision that is seriously out of touch with what the consumers of the world want today.