Special pvp items with for example high stamina (vitality) and damage reduction like in World of Warcraft could be nice (and other useful mods like tenacity from league of legends: reduces the duration of disables stuns and other stuff)
Lets say you would be granted for example starting set, let's call it S0 at lvl 70.
And then you could play arenas for rating and arena points, so that you would be able to purchase let's say next lvl tier S1 for arena points no rating and S2 arena points + rating.
Note that it would require devs to make arena ladders, set items that i've mentioned and few arenas.
/edit: Note that in World of Warcraft alchemy, some engi stuff was disabled during arenas, so why blizzard couldn't disable some unbalanced skills or even just nerf them and try to adjust to other classes.
I am sure that some classes would be obviously better than the other ones but come on, every game has its own op shit class, champion, item or whatever
To sum it up:
Disable all current items and introduce pvp only items/sets
At this point blizzard employees would have to deal only with balancing skills so it makes not so much work comparing to balancing like 200 legendary items. (you will probably say: omfg it's not so easy blablabla... YES it is not so easy for a brand new gaming company, but come on it's Blizzard, they earn so much money i am competely sure that they could employ 50 extra workers only for lets say 2 month period in order to prepare good pvp and then keep current workers only to maintain this.
Copy world of warcraft arena rating and que system etc.
Make some arenas
Players could agree to use only blue or rare items without legendaries.