That's definitely interesting to think about. I think they may keep armor abilities on. Or perhaps turn certain ones off on paticular maps where one ability could provide an unfair advantage. For example, turning off jetpacks on sword base. I think weapons will probably remain headshot only. So that would be Dmr, Magnum, Sniper, and (in place of the carbine) the needler rifle. There could possibly be exceptions, kinda like on Onslaught where a mauler is included, but decreases your speed if you pick it up, or the rockets on The Pit. Are there any other weapon exceptions on MLG maps? I can't recall.
Anyway though, pro players are in for a change up. So many weapons in Reach have changed in the way they can be used effectively. Plus with the addition of things like the grenade launcher (Pro Pipe) and the different firing sequence of the Dmr, people's A-game could be seriously thrown off. I'm definitely looking forward to it though.