Fight for the real King of the King
Why not, we will have a task for level 20 that allow them to create a new account in a unique server. This unique server are only for the level 20s and all KOK in all servers,like PvP, will join in and compete for the real title of KOK.
Obviously, in this server, leveling will not be as easy as the normal server.
But instead, the difficulty should be at least be the same of PvP, in which upgrading only gives 1/3 of the prestige.
The player that is able to maintain being the top in this server will get a some sort of prize/medal/recognition.