I think that as a avatar becomes more and more powerful, more skilled in his arts, he should be able to choose a certain path that will enhance his abilities further.
I am not asking for new classes, i.e: warrior, rogue, mage, healer
If a character wished to go deeper into a certain fighting preference (still be able to use magic, if he or she preferred a more physical fighting style) that they were able progress further into it as they somehow complete a series of quests, achieve a number of /gameplay time, or maybe have maxed out a number of specified skills.
PS- This is just a idea, and probably has been covered and I will be linked that thread soon. Consider this a refresher if this has been covered.