From the videos I’ve seen, it really looks like Halo 4 will have virtually no aim assistance whatsoever! I think that is a pretty good thing, because it will really deepen gameplay and make the choice between the BR, the DMR and the AR have more meaning.
I like the AR, so I like the idea of having a weapon that will be easier to aim so I can focus on making my opponent miss shots. It really does help give you options on how you want to play this game.