Being a fan of the Dark and Nature schools, I'm eager to see the Necromancer and Druid. The Warlock fuels the aggressive side of the Dark school, being Dark/Fire with aggro-y demons, so I imagine that the Necromancer will be focused on more on a controlling kind of gameplay, being Dark with ice spells with tenacious zombies and dead stuff.
Some basic things I think the Necromancer might have:
Spawnpoint: maybe some kind of Tomb that gets bonus channeling when creatures die.
Equipment: a staff that buffs undead seems obvious, or some armor that allows you to move damage from the necromancer onto your undead minions
Conjurations: something cool could be a conjuration that uses a Phylactery theme, where the Necromancer loses some life when the conjuration enters play, but gains a good bonus like extra channeling or more damage or something. Or maybe the phylactery thing could give him extra life for an upkeep cost.
Enchantments: More curses, like one that turns a creature undead. Then another enchantment that would be similar to Mind Control except it would allow the Necro to take control of undead creatures. Call it Command Undead
Attacks: Water spells with a freezing focus have been hinted at in other parts of the forums. Maybe have them deal less damage but have high effect rolls to freeze or whatever. Lots of damage upfront doesn't seem to fit a Necromancer--he'd probably rather just render his enemies useless and let his zombies eat them.
Druid:
Spawnpoint: Something interesting could be a spawnpoint that rewards you with extra channeling for having more and more nature conjurations, kinda like temples for the Priestess but more generally. It would give off a feel that the arena was being invaded by a forest, which is a neat theme.
Equipment: Not sure on this one...Druids don't strike me as really having a desire for equipment. Maybe only one or two, since artifacts run counter to plants and nature in general. Not really sure what they'd do...probably a ring for nature spells, maybe a cloak or armor of thorns for a damage barrier?
Conjurations: Give her some conjurations that can attack stuff in or near its zone, like aggressive plants. She could spend mana to allow them to move, that'd be interesting. Or maybe walls that can attack units that are near enough to them.
Attacks: Vines that push or pull, blasts of harsh sunlight, lots of poison effects. I'd like to see an aggressive Druid that tries to dominate the arena through gradually taking command of zones.
Well those are my expectations...anyone else?