Druid forms change is a nightmare.
Here's druid PvP from now on:
Mage/Shaman polymorphs me. Assuming the nerf applies to shifting out of polymorph as well, I wait until it ends. I spend more mana shifting back into my form (which is essentially required for all types of druid in order to actually use core abilities) than the mage/shaman spend polymorphing me.
He morphs me again. I spend more mana than he spent again.
Repeat until I'm out of mana and he really isn't.