The incentive for people doing open world pvp IS open world pvp, there are areas for it, the den and and every other area in the world not blocked off to one faction or the other. Its the pvp community that either make or break open world pvp on its own community.
If you need a shiney to make you do open world pvp then your doing it for reward and not for openworld pvp.
Personally, I'm saddened that these new PvPers no longer PvP to PvP. I still think the worst mistake in MMO history was to start offering rewards for PvPing. Now no one will do it unless they get a shiney for doing it.