What to do once your 50? Add more levels? Naw, put in place a remort system. Once your max level the option to remort to level one is opened up. It would allow access to special/locked classes, gear, carryover a small stat bonus etc. This was used in some old circle muds and was awesome and kept players busy without having to overhaul max levels of players and content.
A Class Advancement system is being worked on which will allow players to further specialize and customize their chosen class.