I was thinking, to mix up multiplayer/the game, and a new level of customisation, bring in alternate weapons.
An alternate weapon being a remake of another weapon, with different stats.
Say, a Sniper Rifle. It's alternate could instead of having 4 shots, have 6. Where it might take 3 body shots to kill someone, or 2 headshots.
Or with the assault rifle. It might have a lower rate of fire and less accuracy but it could be more powerful.
You get the point.
And using this method, you could choose a preference for which weapon you would use for loadouts. . So, you can choose the default assault rifle, or the alternate assault rifle, for your loadout.
But these alternate weapons could be unlocked after obtaining a certain rank, to mix it up some more. To have more incentive to play and rank.
*Please note*: In no way would these be overpowered weapons. Just a new approach to the way weapons work.