Not so much from PvP I imagine, as there will be for the amount of grinding new players will have to do in order to do well… anything.
“Why does it take me two weeks to reach level 20? I could do that in 20 minutes before! What happened to my exp boost heirlooms? Why can’t I breeze through dozens of mobs on my mage?”
The PvP will just be the icing on the cake. “WTF I get one shot by everybody in BG’s! They’re not even twinks! I’m lvl 21 with quest greens, why don’t I go to lvl 29 anymore? This is unfair!”
I hate to say it though… but I’m going to have to go Alliance in Vanilla because I’m a big time Paladin player, and I’m going to love every second of having Seal of Command back. I’m going to cuddle it, squeeze it, kiss it, and love it forever.