The reason hardware 2fa keys like yubikeys are unphishable is that the browser controls the usb communication with the hardware key and passes the origin of the page to it - the page itself can't spoof an origin. But with WebUSB a page _can_ communicate directly to a yubikey and pretend it's being asked to authenticate on a different origin. It's been fixed now but it was an interesting bypass: - https://www.yubico.c…
Hmm this might not quite be WebUSB territory but it would be interesting to put a Yubikey in the cloud so it could be accessed from anywhere.
What is the advantage of yubikey over TOTP in that scenario though?