I think Disney actually should be doing that, but this doesn't accomplish it. If they want to manage crowds with price, they need to do it with admission prices. Things like this don't do anything to reduce crowds, they just segregate them.
The problem with expansion is that demand always circles back to the Magic Kingdom, specifically the hub and Fantasyland. So they'd be able to handle bigger crowds in total, but those bigger crowds are still going to congregate in the same places they do today.