I really like the idea, Thomy. This might hype others to finally work towards getting 200m exp, but this won't really add any new content to the game if it's just virtual which was my aim for this prestige system. How about a new game mode? Just as JP mentioned, we can call it prestige mode and disable dxp and make exp gain tougher. Players that choose this mode will have a special icon next to their name like crossed swords to show their dedication. We can maybe also disable trading for these accounts, if a player finds it too difficult he can simply give up his rank by talking to a npc to be reverted to a normal player.
Edit:
As far as trading goes, we can also have members choose 1 partner that they can trade with, this should encourage team work. This partner cannot be changed, once selected they will be partners for eternity. (Otherwise players will keep trying to find new partners to find an easier way to max)