I don’t really understand how USB stuff works (what is the difference between a hub, interface, and controller?) but from what I’ve seen I think a hub supporting 20gbps would probably be in the 5-15$ range and probably not larger than a few centimeters

If you have multiple ports driven off the same internal hub, they will share bandwidth.

I’m usually happy with increased efficiency as it represents an increase in performance in the future. Cost is something that seems much more inevitable to go down than performance is to go up, so the two metrics I look for in the state of the CPU market are peak single core performance and performance per watt. Of course, this only applies to observing the industry from outside, I’m sure if I was actually in the market for a new CPU right now I’d probably be happier with a worse performance per watt chip as long as it was cheaper.