[tekchip]

The benefit to folks who flash devices frequently is obvious. However, joe user, the other 3 billion or so users couldn't care less. Poking holes in the sandbox for those folks is negligent at best.

Perhaps the solution is a separate tool, maybe just a separate browser, specifically for this use case?

Flash Browser, heck it could even come with additional tools to help do this. Preconfigured white or black lists, bookmarks to the most common flashing tools, reference material. Make it an even better experience than bolting webusb on to the browser raw.