Alright so we got these kinds of casters so far:
-Necro: Heavy AoE, summonables, DoTs, drains, some control, and typical magic missles.
-Elementalist: Heavy supportive AoE, burst damage, supportive heals, some control.
I can expect the next caster class to have fast casting with light damage, heavy CC in the form of AoE and single target snares, and something very unique. This all sounds like the profile of a mesmer, but I doubt they'll add the mesmer class. I'm hoping for something more along the lines of a mix of ritualist and mesmer with a HUGE twist.