Nerf Wave of Light damage.
Nerf Strafe damage.
Nerf Haunt damage.
Nerf Ground Stomp duration.
This is a good part of why pvp took so long / never really arrived. That said, personally I would say it's a very bad direction to start nerfing pve skills for pvp balance.
As to Path of Exile, we'll see if PoE is the savior some claim it to be -- I'll play it and I'm sure portions of it will feel like, "why didn't blizz do that". Other parts will feel like, "man, blizz did this a ton better." From what I've seen of it on youtube, the combat doesn't look very fluid but it may be fun to mess around with the skill tree and other systems. Whatever the case, I'm fully confident that Blizzard is/has been watching and will take the good parts that make sense and improve Diablo with them. No, I'm not saying we will have a poe skill tree in D3 -- but I would not be surprised if they have people working on a map system to expand the D3 end game.
Copying the copiers is something WoW did over many expansions -- whatever competitor popped up, they'd mine it for the good ideas or innovative systems that would fit within WoW and improve their game. Over many iterations of failed competitors and new features put into WoW, this makes the wall to climb all that much higher for future competitors. Pretty sure, you'll see much the same in D3 and personally I look forward to where D3 will get to over the year(s) as these improvements get implemented.