If you really think about it the 9 classes pretty much cover any other class you can think of... Necromancy is one i can think of which isnt really there (a necromancer or anti-paladin class perhaps). Trade skills also take up the space where classes could have been (Tinker = engineering, Alchemist = alchemy, Weapons Master = blacksmith).
Things like rangers and specialist hunters (demon, shadow etc.) all really go under the hunter class and will probably be given to hunters of high levels after training. Same for other thing - Mountain King = High lvl Dwarf Warrior, Knight = high lvl human warrior, Priest\ess of the moon = high lvl priest. Making more classes would perhaps clash with classes we have already, i mean every area is virtually touched upon...