Imagine having your profession upgraded by your level and achievements, lets take Warrior Class for example, for each set of level you can upgrade your class, and willingly switch between your old and new. Your Class varies depending on your affinity, like good or evil. The classes you can get can also depend of the gods you are associated with:
Good: Warrior(Lvl 1-25 Starter Class) -> Paladin(Lvl 25 -70) -> Titan(Lvl 70 – Max)
Evil: Good: Warrior(Lvl 1-25 Starter Class) -> Beserker(Lvl 25 -70) -> Dark Titan(Lvl 70 – Max)
Same could go to the other classes, Like Elementalist can lvl to Wizard and Theif can lvl to Assassin.
Sounds crazy but to me it makes the classes worth leveling up, without being stuck with one like forever. So what do you think?