We dont know yet.You're asking questions too early about this too early.halo 4 isn't out yetHalo 4 seems to be on a new planet. Most likely a shield world. I doubt Elites will even make an appearance, at least not until Halo 5 or 6, if Chief is to be rescued. Furthermore, not enough info has been gathered from Halo 4, except from the trailer and the teaser posters. Your question is unanswerable except by someone involved in the project and those people are unlikely to tell us for quite a while.
Well, actually, in a gameinformer magazine for halo 4, there will be the convenant. But also another alien race (Spoliers!)
Actually, they stated that Elites will NOT be playable and armor "upgrades" will be available.