*Have a ranking system like we had in vanilla wow.
*Each rank will unlock a title / achievement (if any in the game).
*X ranks will unlock vanity items and stat-less gear and weapons so they can show off their awesome looking, unique pvp items. (a transmog type feature would be needed).
*X ranks will unlock abilities specifically designed for an pvp encounter to give them a small edge over someone who just occasionally plays pvp.
Those are a few things I can come up with at the top of my head, got any suggestions yourself?