First off I would just like to say phenomenal game!
At the moment the only improvement I can think of and would like to see are Raids. I honestly love your PvE, absolutely amazing Dungeons(Love the Challenge!) but gear upgrades are much needed and Raiding would be wonderful with this combat system.
Now before the PvP people start getting angry there would be a easy solution to the problems it could and would cause in PvP, all you would need to do is make it so Raid Gear is not Equippable/Usable in PvP. You may even say or think that Raid Gear would make PvE unbalanced and unchallenging, so if that would be the case you could just make Raid Gear only usable in Raids.
This way you can still have the Raids a lot of people love, and the Gear Progression a lot of people enjoy, as well as Raid Progression, because you would need the Gear from the Previous Raid to be able to stand a chance in completing the next tier of Raids.
And you can have all this and still not hurt any of the other PvP or PvE if done right. 
I really hope that my suggestions are looked over and if not used at least commented on by the devs.