They won't do this. That is part of what made D1 hard to balance. They would balance shotgun/sniper power by using ammo as a way to regulate their use, and people bypassed that restriction by using Universal Remote and NLB in the primary slot. They've learned their lesson - that exotic special/heavy weapons in the primary slot make the game impossible to balance for PVP because it allows players to get around ammo restrictions. Therefore, since they've remade the entire game to make it easier to balance PVP, they simply won't repeat this mistake.

I see your point but with the weapons having specific perks they could target that weapon for adjustment. At least in theory.

But that doesn't get around the fact that weapons in the primary slot run off of primary ammo. This is what effectively allows a gun like NLB or UR to get around special ammo restraints. So even if you can target a specific weapon for nerfing, it doesn't stop the gun from bypassing the ammo constraints which keep that class of weapon in "balance" in the first place. If they DID allow for non-primary weapons to slide into the primary/energy slot, they would have to be nerfed to the point that there is no difference between that weapon and other primary weapons. At that point, what is even the point of using a sniper/shotgun/fusion rifle/etc in the primary/energy slot? If they're no more effective than other primary weapons, there is no advantage to doing so. And even beyond that, they will be so weak that nobody would want to use them in the first place. The bottom line here is that it makes no sense to rebuild the ENTIRE system for PVP balance, and then implement something that is going to ultimately ruin everything you worked so hard to create. I.E., weapons live Vex Mythoclast, Universal Remote, No Land Beyond, etc. aren't coming back. Primary weapons will ONLY go in the primary or energy slot, and Power weapons will ONLY go in the power weapon slot. There will be no mixing this time around.

I see what you are saying. Having something like NLB circumvent the usage restriction the Power slot provides would break the balance they are going for.