I have no interest in this game including PvP, and I think it would be a mistake for developers to include this and devote resources to it.
With multiclassing and 10 classes that is really something like (Sigma) 1-10 or in other words 1+2+3+4 ... +9+10 which is a total of 55 possible class choices (like Paladin/Wizard or Rogue/Barbarian or plain Chanter).
Trying to balance PVP so that all of these class choice possibilities are viable, if played correctly, against every other correctly played combo would be a nightmare. Either it would take enormous time and resources (if done right), or it would lead to a real dumbing down of builds and spell/ability combat mechanics if done the "quick way". Neither way would likely ever work well. And this is not even taking into account character levels, do we want it to also be balanced so that every level 10 build (if played correctly) has an equal chance against every other level 10 build? That would add another whole dimension of complexity.
The only way to do PvP in a game like this would be to ignore class balance and say things like... so what if every Wizard, Druid or Wizard/Druid can always kick every ranger's and rogue's ass with ease, every time? But then, what is the point of PvP? it would really not be much fun for the rangers and rogues, or the Ranger/Rogues, ever.
So that's a very strong No vote from me.
No need to do this at this stage, it's more about extension or a mere possibility.
I see this option more for the endgame, when you've done everything and would like to test your champion vs other try hard people.
For me such games are only good at their hardest achievements, like "The Ultimate", which I could achieve only with wizard.
So I guess wizard is the best vs the game content, but how will wizard class do against others - that's the question we will never know, assumption is the only thing.