It is in no way, shape, or form cannon to... well... anything... but I'd like to see an animal aspect sort of "altered beast" type of form or series of forms find a spot somewhere in the game (either with the druid or through another class's spell).
I think your idea about going more truthful to the class and letting them add forms as they've encountered creatures is quite genius. They should definitely look at doing that.
They should also think about adding a few hidden gems in with the class. Places that only animal form X can reach. Perhaps an unintentional and possibly heart wrenching romance with the territorial squirrel in the grove (a la Disney's take on King Arthur) if you happen to approach while in the form of a squirrel.
Perhaps, if the druid goes to sleep while in animal form they can get the bite encounter with Astarian a bit earlier than normal.
I'm just throwing ideas out there... but the possibilities are virtually limitless.
