I love this idea, and think it should go forward. I've read this thread and the reasons against it are far from anything that can be called a negative. Just what you believe Blizzard is either a) unwilling or b) unable to do.
I've advocated for this myself. More specs and less classes.
Also, I do not believe that they would implement them all in one expansion, but over a few.
Add 3 in 1 3 in another and 4 in the last. Or perhaps over a whole expansion.