Running around a keep invisible isn’t easy. You have to stick to certain areas, guards can detect you if you get too close, and there’s a always the risk of turning a corner and running into an enemy player out of the blue.

You’re only thinking about this from a defensive standpoint. Imagine trying to attack a keep that has twice the number of NPCs, who all have a powerful stun ability and multiple debuffs. Have you ever tried to take a resource solo, only to have someone jump you and kill you with the help of the guards? It would be that, but twice as bad.

Besides, with all due respect, I don’t need my game to play itself for me. I can pop detect pots and defend a keep from wannabe ninjas just fine.

Better option would be GUILD AP, so that the people claiming the keep could upgrade the keep with more guards, oiling guards (over doors or over flags or both for more ap), a backflag special guard, "lord of the keep," of guilds choice (sorc, nb, etc), stronger walls, stronger doors, etc