I think now is the perfect time for Halo to move towards a more Battlefield type of experience. The multiplayer being more in line with the epic battles that take place in the campaign is just the type of shot in the arm that the series needs to challenge the CoD series.
Look, I went to tournaments in Halo CE and Halo 2, I love the more traditional DM aspects of these games, but they've reached a wall with those mechanics. You saw Bungie grasping at straws in Reach with the armor abilities and the tacked on Invasion mode but it came short. If Halo 4 makes a jump that's similar to Reach (more of the same with great add-ons) its just going to be another blimp on the radar and get beat out by random CoD game #7 made by Treyarch.
CoDifying the series or better yet looking more towards Battlefield would be a great idea. You start with JIP for sure.
There's such a rich opportunity by going with brand new mechanics. The lore already supports
a wide amount of class systems that you could envision (ODST's, Spartans, Elite Zealots, Jackel snipers, etc), and by this point even a variety of different weapon systems (DMR, BR class weapons, multiple pistols on human side, AR's, etc).
Personally give me Battlefield: Halo with the innovation and more twitch based play that Halo's mechanics and shield system bring to the table. You bring that to the table, firefight to go with it and 4 player coop...I'm drooling.
Obviously a lot of fans here will disagree. Personally I think they've gone as far as they can with the old mechanics. I can't imagine those old mechanics being iterated for ANOTHER trilogy. I mean...how long do people want to keep playing one of those games? Halo Anniversary should be the nail in the coffin for that stuff.
Commence flaming.