Hmm. It would certainly add an interesting dynamic to the Dragon fights. I fully support the idea of a mod that does this.
It would add such a layer of awesome to dragon fights. Instead of the following:
Step 1: Avoid or tank their fire/ice breath attack.
Step 2: Avoid or tank their bite/claw attack.
Step 3: Hit dragon until dead.
Alduin does a fus-roh-dah during the Helgen attack right when you're about the be beheaded.
He also summons the firestorm. Whoopity do though. There are dozens of other dragons in the game that do nothing else.