Short version: For the most part, the Y seats on the QF B787 suck. But nothing will be changing no matter how much a small segment of the population complains.
Longer version: Most airlines have done exactly as you suggest: Y+ (or W if you prefer).
Are you perhaps saying though that the price point currently charged for Y+ is too great a jump from the regular sardine can Y? So potentially you're not seeing that as the answer to what you're after with the better Y product?
Airlines operate in very thin markets and know EXACTLY what people will and won't pay for. As first generation Y+ cabins or aircraft with them are coming up for renewal/refurbishment, they're generally being expanded. I'd suggest that the initial foray by most airlines into the Y+ market was with cabins perhaps a little too small, and that many are expanding the size of the them as they get the better data on what their markets will bear. They are, in effect, coming around to your way of thinking. But, they're going to extract as much profit from that change and if the market continues to pay for the Y+ cabin in Australia at double the cost of the regular Y cabin: well that's the cost of that extra space and comfort.
How much is Main Cabin Extra on AA above standard Y? I doubt QF would go down that path as they already let you pay extra to choose seats or other customisable elements of the flight and that's far cheaper than further modifying the hard product.
Y exists in the shape it currently does because the market will bear it and all the complaints in the world won't change that. Many people hate Ryan Air and Jetstar, yet...
...and thus threads like these go.