SOE claims to have content planned and/or in production for expanding the game up to I think level 200 (maybe higher, I forget). I would tend to think that each class would get an even more defining sub-class or a class specialization.
I.e. Shadowknight at level 60, gets the choice of advancing different aspects of the class, such as: Defensive Melee, Offensive Melee, Offensive Casting, Defensive Casting, Utility, Undead Control, etc...
This could be done by another class selection. A "Grave Lord" will be mroe intune with handling undead. A "Corpse Destroyer" would be more offensive, while a "Black Guard" would be more defensive. Those are just some ideas and hopes I have for the future.