At this point, I'd rather have 10 polished classes than 11 or 12 classes that are hugely imbalanced against each other. Maybe if I had a really good idea for a new class, I'd feel differently. But every cool feature I think of could easily be applied to an existing class. Also, I have yet to see anyone post a great new class idea on the forums. Such a proposition would have to be REALLY good on paper, this is WoW after all.