I want to see them expand even further on their single-player.
-A more nuanced, sweeping story that calls to mind Gundam or Macross.
-Better level designs that make use of parkour while shooting, similar to the training course. Also alternate paths through levels.
-Doubling down also on the Nintendo-esque use of level mechanics, including for the Titan
-Co-op.
For multiplayer, though, honestly, they can just build on what they have for 2 or go back to 1 and improve matchmaking. Though I would prefer an alternative to grinding to unlock stuff. The CoD4 model has overstayed its welcome.