A high rate of fire, high damage assault rifle would be a bit overpowered. Lower damage is what balances the higher rate of fire. They can give it less range, but then it becomes considerably less useful. It would depend heavily on the recoil.
I wouldn't mind seeing a true revolver. Just give us a Magnum. Timeless. Classic.
I don't want anything like the Stoner63. That thing had stupid recoil. If anything, make it so the grip is actually relevant. It used to be somewhat of a requirement on LMGs, but it has such a minuscule affect that it's pointless to equip.
There's enough sniper rifles in the game and each one has its niche. I don't think adding another sniper rifle makes much sense.