PvP would be possible, however the damage calculation would have to be handled by the interserver as it could not be guaranteed all servers involved in the combat would agreee upon damage. Also the possibility of less honourable server admins "pimping" up characters would make things tough to control. Also, a free4all server for instance pvping with players from a leveling server would be vastly unfair. For those reasons I think interserver PvP would have to be non-serious, i don't think tournaments would be acceptably fair.