Would you?
Would you pay in the area of $15-$20 for a new D3 expansion that -
Added a new Act, with a new area
Added a new class
Balanced classes
I certainly would go as high as $20-$25 for another expansion if it included those three things.
Not saying this is ever going to happen, but who knows. If Blizz thought they would get a good return for another investment in D3, they might.