Social is missing the fun party modes. I wanna see Grifball, Infection, Crazy King, etc. in the game ASAP.
Customs browser needs to be in the game in the near future.
Ranked needs at minimum a 2v2 Slayer playlist, an FFA playlist and an Attrition playlist. Also make ranked spawn with one grenade to promote more scavenging and not having the free ability to nade spam off spawn. Also with Attrition, setting the rounds to 3 to win and the revive time to 1 or 2 seconds really helps the mode play a lot better.
Social features are missing from Infinite. Pregame lobbies would be nice, along with the map veto system and party up features. Good service records which displays ranks, K/D, games played, time played, campaign stats, etc. would be great, with the ability to view other peoples.
Firefight should definitely make a return in Infinite. Its a great mode to have as something different to play, lets you play PVE without being locked to story missions/open world gameplay and is a great splitscreen mode.
Some form of XP levelling system (separate from the battle pass) needs to be introduced. It doesnt really matter which variation of the system it is (H5/Reach/3, whatever) as long as one is introduced soon.
I think challenges should be allowed to be passively completed. So rather than having 4 active challenges, all your challenges should be active at once. That way you dont have to sit for hours trying to complete a challenge that you could have gotten ages ago but it wasnt active.