I imagine everyone can use every gun, with no class specific object (except for armor). Instead, specialization skills you get with levels in your class mold what you should be doing. You get bonuses to some type of heavy powerful weapon with a Enforcer, you get it with Assault Rifles and Support Rifles (assault with a scope) etc. And the skills boost your damage/rate of fire/accuracy/range etc. Weapons shouldn't be prevented from use from any class. An Enforcer could be able to use a Sniper Rifle, just have a horrible time finding a good kill spot because he lacks proper methods for finding them, or his armor reduces his accuracy (which wouldn't significantly impact a RPG or Shotgun)
Knowing that the games also half PvE there has to be some sort of method for 'aggro control' which will probably come into play in PvP in some form. Stop thinking inside of the box
the games not you're ordinary FPS, you have character levels complete with skills and dozens of weapons and a sleu of PvE attributes to take into account.