This seems a little far fetched to me, but apparently when ensemble studios shutdown (Halo Wars, and they were supposedly working on the Halo MMO called "Project Titan"), some of their employees went to Blizzard. Now Blizzard's MMO is being referred to as Titan. Is Blizzard doing a Halo MMOFPS? Or maybe something just different, but similar enough to see the roots, like how they pretty much took everything in Warcraft from Warhammer.
I think their might have been more "evidence" to this rumor, I don't remember. But basically that rumor is that Blizzard is making a Halo MMOFPS, or the same game type in a similar world.
I really hope this is all bullshit though. MMOFPS from BLizzard? Sure. A Halo one though? No thanks.
