I would personally like a big Faction Wars type of PvP , similar to the world vs world in guild wars 2. I know it's probably impossible, though. It'd also be really awesome if we could have all the regular halo-esque playlists like CTF and Slayer (hopefully they can still call it slayer), while also adding new stuff. Specifically, something like Invasion, where one team is attacking and the other has to defend. I really hope they'll break some new ground in the PvP area.