25% exp bonus. Special titles with a fame decay system like in EQ2 pvp. Allow players to toggle pvp flags with a 4 hour lockout between toggles.
Just get all your fellow PvPers together and have them flag red. Surely you can manage to get 2 guilds worth of PvPers to join? Then you can have your little wars and still have people to group/raid with.
If you enter an instance via AoC, All red characters are reverted back to blue. Raiding is a non-issue.
So, why do people need an incentive? Surely if PvP is super amazing folks will flag just to be able to participate in the fun.
I feel like the best incentive they could offer wouldn't be for the character that is flagged PVP. They could try what they are doing with Vaniki and associate a claim reward across servers with your PVP achievements.
Sadly EQ PVP has been neglected over decades and the PVPers have long faded away... That said, don't underestimate the amount of interest in proper PVP games, it's a blockbuster industry... but to bring back EQ PVP or even EQ2 PVP.... I think would be hard. The best bet if to enable PVP, with the option to revert to blue and revert to red at will... with special content added to regular servers so as not to impinge on bluebies... make certain raid zones pvp enabled... make certain OW Bosses pvp-able... make special loot drops with pvp stats, titles, and guild wars style and group competition open... so that, say a bluebie guild could play red for a day to try it out and revert to blue if they didn't want to play red all the time. Something like this would be a lot of fun, be very popular, and bring back a lot of old time EQ pvpers without taking anything away from the basic blue game.