I thought about that, but considering the work they did on Combat Evolved Anniversary, where they pretty much reworked all of the visuals in the game to be entirely new, and altering the cutscenes to be animated much more smoothly, they would probably attempt the same for the rest of the games. Halo 2 and 3's cutscenes were a whole lot better animated than Combat Evolved but they would most likely still reanimate them. Plus, they might add more secrets and easter eggs to the games, and then, if they include multiplayer, even local, that's a whole lot more.
If 343 was to do this, I wouldn't expect them to create a simple port for all of the games.