A lot of the suggestions here are boringly generic, impossible to implement or blatantly obvious. So I'm going to post some ideas that are actually implementable and probably useful:
Ranked-based matchmaking for 2v2/4v4/6v6 competitive playlist (championship ladder system).
Please do not make melee overpowered (one-hit kill with full power to armor), a knife should not win against a bullet.
Please bring back Powerstruggle game mode; everything in Powerstruggle should remain the same, such as being forced to make kills to purchase more powerful weapons and vehicles (Battlefield & Halo simply spawns them for all to use and then they are then rendered a novelty to those who use them RATHER THAN BEING A TOOL TO THOSE WHO EARN THEM).
Add a hardcoe mode (call it EMP Mode, where an alien EMP has disabled all human electronics for invasion) for people who want to play tactically. Armor and suit functionality is disabled (the HUD will display an immersive error message from the nanosuit). You cannot see your ammo count unless you manually count it yourself. Bullets directly damage health, no automatic healing, no killstreaks, no vehicles, no minimap or radar. Just your skill and your mind.
Please do not allow killstreaks to be stackable, they should not be easy to acquire, they should allow for the losing team to catch up and not allow the winning team to steamroll the losing team. Allow them to be called in at whatever sequence the player wants (do not force them to be called in from the last one earned using only a single dpad button à la Call of Duty)
Please allow for players rank to DE-LEVEL based on bad kill/death or win/lose ratios so rank would actually reflect individual SKILL rather than reflecting TIME PLAYED.
You do realise you just said " a lot of the suggestions here are boringly generic, impossible to implement or blatantly obvious" and then asked them: to put in your hardcoe mode which takes away all the nanosuit features and makes the game generic, to implement a whole game mode from crysis that completely goes against they're new mp vision, to put in vehicles after they've already stated that vehicles wont be in mp and a whole new leveling up and rank system.

also the nanosuit 2 is emp proof.
OH NOES! I thought of a EMP Nanosuit Module. D: BTW Merry Christmas to all!