I'm fairly certain they have actually confirmed this in a roundabout way. You see, there will be the standard playlists (Team Slayer, Team Objective, etc) which will contain maps (and therefore the relevant sandbox and settings) from all 4 Halo games. So in Team Slayer the lobby might get 3 options: Sanctuary (H2), Valhalla (H3), and (sorry can't remember Halo 4 map names, quit playing it rather quickly). If the lobby votes for the Halo 4 map, then armor abilities and loadouts will be present, but if they vote for Sanctuary then they won't.
Then there will be a dedicated playlist (at least one, maybe more) for each game. So, say, you choose Halo 2 playlist, then the lobby options might be to vote for: CTF (Sanctuary), Team Slayer (Turf), and One Bomb (Zanzibar).
What I DON'T think you'll see is dedicated playlists for each game in every game mode. AKA I don't think we'll see H2 - Slayer, H2 - Objective, H2 - Swat, H3 - Slayer, H3 - Objective, H3 - Swat. I think we'll just see TS (all games), Big Team (all games), Swat (all games), Team Objective (all games), H1 (mix), H2 (mix), H3 (mix), H4 (mix).
I seem to recall the SDCC panel actually showing a video (or maybe it was E3?) of the pre-lobby where you could select which playlist to search and it was essentially this sort of setup.