How can they add more classes and make them unique and have their own flavor?

[RocheKat]

WoW has lots of classes with 3/4 specializations each that all play very different. Part of what makes each job different is their story, the weapons they use... there are lots of options still. For example right now the three melee don't really deal with procs so a melee could be added that works more like MCH or BRD. We also don't have a melee magic user or a support melee... I am honestly expecting RDM to be a melee magic user with support.

Making dps different isn't very hard really, Healing is a little harder and tanking is probably the worst. The reason for tanking being tricky is because you cant have a lot of RNG in tanks. You can't have a tank threat/mitigation level changes randomly because they would either not be able to do their job or be too powerful.