That's a great way to kill adoption of a feature. But what has WebUSB done to you?
Existing. HDR is also on the list.
Why? The permission dialog is crystal clear.
It's only sorta ok right now because nothing uses it normally. If it were used mainstream for some legitimate purpose, that permission dialog would get ignored, and it'd become a security risk. USB isn't something web needs to touch unless you really know what you're doing.