Personally I'd like to see the brute shot and smg back.
as far as new things go I think that if they could do something like Destiny and have an A.I. like the ghost which could update objectives and waypoints but it mightn't be Halo style however it could be like in Halo 3 where you had Cortana in the last level but it's more useful. Also what's your thoughts on if they had an A.I. system as a guide like the ghost from Destiny