That's an interesting idea - normally we associate with these days Arena matches, but having something more "Massive" going on Otha could be interesting.
The only goal really would be to get as many people as possible on each faction and see what happens. There would probably be no winners, and as it s an open instance, you could not guarantee that only "official" players would be there.
I would definiely suggest that as a minimum, should instead be opted for a more traditional series of Arena matches, that every Arena player has to be on Otha while not fighting in an Arena
I like this idea.
But are there zones other than Otha? I only ask because in case of NPC aggo, it's annoying to have to remodulate your weapons every 3 seconds.