Not sure what you mean by any hashrate. If your hub is powered and is min 3A, that is sufficient to run Hex full speed as in my post above.

I guess he might have meant "what happens if I plug it into a standard USB 3 port? Will it hash at a lower rate with lower current, or will it not work at all?"
With possible follow-up question "what if I plug it into a USB charging port on my computer?" (the answer to that, depending on the above, being "check the maximum current it can deliver, it might be noted near the port itself or you should be able to find it in your computer's documentation/motherboard manufacturer's website)
Yes that question. Is it possible to operate at any hashrate if you plug it in a regular usb 2.0 or usb 3.0 directly on a computer motherboard? Not in a usb hub. I know usb 2.0 can provide 0.5A and usb 3.0 around 0.9A (?) so, will it hash, at what speed?

Yes you can plug it in to any hub and it will work, or at least on most, so far i haven't found hub that doesn't work. The lower the current is the lower hashrate will be. I don't have any low power hubs below 2A so I can't tell you what hashrate will be. 0.5A is normally per port and if your hub can share current between ports without limit you shouldn't have problems with power on pretty much standard hubs. If you are going to use it on pc, usb 3 hub will work well, most of them are over 2A.
Hex works well on hubs 2A+, usb2 or usb3. ( on PI only usb2) . I cannot guarantee how it will work on hubs below that so its up to you guys to run it on setup that will meet the requirements. As I said should still work but not sure how well.
In fact, Hex hes been designed to be tinkered with so you should use adjustable external power for you hub, and this is when you will see its full potential.