There's some debate about that on irowiki. In my opinion, at least 3-1 classes should be implemented (the older ones especially like Rune Knight, Arc Bishop). Some 3-2 classes like Genetic and Soccer, we have yet to see any official sprites. So, highly doubtful all classes will be implemented come June 17th.
Why do I believe some 3rd classes will be made available in the coming maintenance?
- You can reset skills/stats once for FREE
- You can continue to level up pass 99 to a new max base lvl of 150
I'm a bit surprised that this came so soon.
They are actually behind schedule by at least a year.