Extra Polymorph Effects! Polymorph adds in tons of new possibilities for mods, from my lichdom mod in progress to a mod where maybe you turn into a thaumite swarm and unleash the bees on people! Perhaps even be a leprechaun! I was thinking of expanded uses for the polymorph effect, especially in allowing you more freedom to use skills outside of the tree that the polymorph happens to reside in. I think there's a lot of potential for mods that revolve around the caster taking a different shape without having that shape necessarily be limiting or even have selectively limited powers like embracing one's dwarven heritage disallowing spells based on requirements (such as mana) or specific spell types.
This is a wonderful, well-thought-out and descriptive suggestion. Perhaps you should actually suggest something.
So here's an idea, how about "stance" mechanics for polymorph? Kinda like Udyr in League of Legends, though i don't think it's quite possible to choose a skill in a skill line without following the progression order