I noticed 343i is setting up something, an evolution, they aren’t going overboard, but I was thinking about going forward with halo 6, 343i is going the route of more indepth squad play. Not Rainbow Six depth, but a natural evolution without completely overhauling the series. I don’t see the squads in halo 5 killing the other off completely, some may survive or all of them, and the Arbiter even, it’d be great to be able to customize your squad and mix and match Spartans and Elites from both into a squad of four.
Halo 6 could bring in some legendary MIA guys from the books into the mix with various skills and loadouts. Custom armors, skins, AI behavior tuning, more advanced order commands, Spartans from Reach that died using a new game plus mode even. Obviously coop would be even more fun. Wantto play team lead as Buck? Fine, do it. Want to use all Elites with the exception of MC? No problem. More options are there.
Not only that, a progressive feature could be customizing loadouts, perks, and behaviors of each. Keep it simple, not a full blown rpg, but some light elements, but also have a selection were the casual halo player is given a “recommended” loadout crew.