There are many things wrong with this design:
1) For it to be equitable, every time a PVP or PVE tier is released, then BW will be forced to release a new tier of the other which has the potential to increase the speed of the gear grind.
2) For it to be equitable, they will have to ensure that PVP players and PVE players are able to gear equally as fast (or slow) as the other.
3) It will not go over well with the PVE'ers that PVP'ers can "AFK" or "lose" their way to the gear they were required to defeat bosses for.
4) It will also not go over well with the PVE'ers that PVP'ers can farm similar gear to them through PVP and then with potentially zero PVE experience jump into high level PVE groups.
5) Then you have the issue of people farming PVP weapons to PVE with since it has the potential to reduce "waiting for a drop" off a boss.
I'm sure there are more.
I understand the spirit of what you are saying, but you need to look at it more realistically.