So a while ago I read that hidden classes will probably be limited to a small number of players per server. I don’t mind this to be honest.
But consider this. In a years time, all those hidden classes will be full, and a lot of people with them might not even play anymore. So basically no one will be able to become a hidden class anymore. So my suggestion is a simple one.
Every week, 2 weeks, month or so on, there is a contest of some kind held. Maybe a tournament, a test or something to this extent. Only people who meet the requirements for a hidden class can take part. And the people who finish this event with the best results are allowed to change into a hidden class, everyone else has to wait until this event is held again.
What this does is keeps hidden classes limited as only a small number of people per week/month can become this class, but it doesn’t forever restrict people out of the class. It also promotes healthy competition among players and gives them something to strive for if they want to become better than anyone else.