I don't like the idea of diverging PvP and PvE where separate gear is required. Make it fun, make it semi casual with some decent rewards. Keep the focus on good PvE.

Making PvP only gear means you intend to support pvp to a very high standard, making it central in the game.

1) Much like WoW pvp, a new stat would be needed (resilliance) to separate the gear.
2) Substantial balancing for skills would be continually required to maintain both PvP and PvE balance.
3) People will then insist that PvP give equal XP to leveling in PvE.
4) Many PvP battlegrounds will need to be made to appease hardcore PvP players.
and the list goes on...

You make PvP a completely separate entity, and people are going to expect you to support it to the very end. Even at the cost of good PvE, and I would much rather have good PvE over half assed versions of both.