I'm thinking it would be nice to have something similar to how Sentinel Super Reflexes works with Master Brawler vs Practiced Brawler.
For those that like their Tri forms or Bi forms, they can pick their normal shapechange preferences, but for those that want human only, they can choose an alternative power instead.
The Dwarf form option could be something like an auto-power that either provides defense, regen, or increases hp, but spreads out the status protection to other toggles. So choosing either that or the Dwarf Form at the level would lock out choosing the other option later.
The Nova form option could be something similar to dual pistols ammo changing that adds different status effects, or damage types to your regular attacks. Of course, choosing that would lock you out of being able to choose Nova form.