An interesting concept i have in mind, combined classes.
For a large fee, you can combine certain classes to get advantages of both classes.
If this idea was ever presented on the server, i'd like the cost to be $5000T for the combined class, and have mastered both.
and to reduce lines and lines of code/text etc, just make certain classes only compatible with other certain classes.
for example, a paladin cannot combine with an architect because they aren't of the same type, however a hunter can combine with an architect because they both came from the rogue class.
another way to reduce lines of text, perhaps instead of 'class' trainers, have 'skill' trainers instead. if you dont have the Ability to train the skill as your tier/class wont let you, perhaps a Heavy cost for the skill you want to learn.