I have a feeling the Timewalkers or something closely related will be the next class. Why?
Weaver Belmaril. Watcher Bianca. Warden Virgil. On the Timeless Isle. Right by Wrathion and Co so you go and get a nice long look at them and their dialogue.
Why?
The 3 of them stand together on the Timeless Isle doing nothing, just talking about their roles in the Timewalkers (and soon to be specs).
Weaver Belmaril is the healer talking about how he heals the timeways. Warden Virgil is the tank, even specifically saying he protectors the others as the do their tasks (ie roles). And Watcher Bianca talks of how she scouts ahead implying some degree of forward action so she would be the dps and probably a caster at that given her staff.