New article by venturebeat:
One interesting quote
How will matchmaking and rankings work across four different games?
Players will have a single ranking that spans across Halo 1-4 for matchmaking and showing-off purposes.
edit: And this quote about controls
Will controls change from Halo to Halo?
Yes — unless you opt for one of the universal controller schemes that The Master Chief Collection will offer. You can just pick one setup and use that for any Halo that you jump into, so you won’t have to worry about buttons that change from game to game.
We have confirmed, though, that Halo 3′s specific controls will not be available as a universal controller option. Its left hand/right hand setup just doesn’t play well with the other Halos.