Depends on how much they already did. If it's just the engine and stuff, then that's fine, but if they already started implementing stuff that people didn't like in Halo 4, they would either have to scrap them, or be lazy and just keep them in the game.
I hope they keep tac and support mods, and maybe add another one. They'd be an awesome way to add to customs, especially if you could tie them to trait zones. Sure, they aren't great in a competitive environment but they've got them in the engine now, would be a great customization option for customs in future games.