The mezz type of nanos are today useless in PvP since don't do anything...
And thats a real problem since some classes combat power stems from the fact that they have them...
There are two solutions to this, 1) Make them work in PvP as they do in PvM. 2) Just remove the current fighting target from the target of the nano.
I think nr1 would be too destructive, so I would say that nr2 is a better solution.
It would still offer some crowd controll for those classes but at the same time not make them overpowerfull...
How it should work....
Player A starts to attack B (with mezz)... B casts a mezz on A. A's current attack finishes it's attack and he drops out of combat.
For A to start hitting again he just have to select B again and press Q....
If that too powerfull also, one could just let A drop out of combat, and not dropping his target altogether.