Or why not just make WM like Monk's Fist of Fire?

That way:

-Empy n Iron Jaws can still be locked behind WM.
-AA is still off while WM is on.
-all skills can become instant cast again.
-Bards can move n shoot again.

(the same thing can be applied to MCH as well)

and make everyone happy (hopefully).

just my 2 cents.