In the pic I saw of the Druid, she was wearing plants (think poison ivy from batman). I'm pretty sure she'll have nature with an emphasis on plants. Not sure about her secondary school...although holy or, like the wizard, 'chose an elemental' school could work.
Im still willing to bet that either the Necromancer or the Druid will only have 1 school trained.
Looking at the first 6 mages:
1 School:
Priestess- Holy+none (can remove conditions, gain life with holy spells. high channel/low health)
Beastmaster- Nature+none (can make pet, quick cast creature, Battle Skill. low channel/high health)
Force Master- Mind+none (force pull, built in deflection. high channel/low health)
2 Schools:
Warlord- Earth+War (Vet Tokens, Battle Orders, Battle Skill. low channel/high health)
Warlock- Fire+Dark (curse weaving, make reaper, Battle Skill. low channel/high health)
Wizard- Arcane+Wildcard Element (Voltaric Shield, Arcane Zap. high channel/low health)
So, its pretty even split throughout. Seems like for every mage with 2 schools, theres one with just 1.
Other fun things to note-
-All mages with low channel/high health have Battle Skill, and can improve a minion(s) (Pet, Reaper, Veteran+Orders).
-Wizard is the only mage who not only gets to choose his secondary, but also has no triple cost "opposite" Making him the most flexible in terms of spellbook cost control.
-Beastmaster Is trained in nature, and pays triple for Fire. BUT, Warlock/Wizard trained in Fire doesn't pay triple for nature. Whereas Dark and Holy are triple for each other in both cases of Warlock and Priestess.
Warlord pays triple for Arcane while trained in War/Earth, Wizard who is trained in Arcane does not pay triple for War spells. So it seems that the "opposite" spell cost penalty is bound to the mage archetype, not the spell schools arbitrarily. So Druid may not share Beastmasters 3x Fire cost, and Necromancer may not share Warlords 3x Holy cost.
-Mages whose archetype starts with "W" have 2 trained schools.