I'd love if they had a chance to start with different abilities like someone said already- some with summon guardian wines, some could entangle, some charm, some could summon wolves...
In fact, why was summon tiger ability removed?
Could we have druids shapeshifting into bears? (In addition to combat promotion, they would get enraged, empower 1-5, heroic strength I,II, regenerate for free while in bear form, but transformation would take 1 turn and they couldn't cast while bears.
Even better, transform into hawk. As a hawk, he could 'rebase' (and therefore travel into any your city or on ranger) in a single turn, then transform back. I don't know about AI though.
EDIT: Bear Druid would retain its nature affinity, and with heroic strength 1,2 and free promotions he would be quite powerful.