Just a heads up that the WebKit team hasn't weighed in, and Mozilla does not intend to look at this specification at all in the near future. So this looks like another Chromium-only feature for the time being.
If it's ratified and becomes a standard however, THEN they can start working on implementing it. But until then, nobody can slag off an implementer for not implementing a draft.
Just like "update the firmware of attached USB MIDI devices via the web, without a permission popup" was something Chrome implemented, and after quite some time had to realize this might not be the best solution.
Sometimes you just have to stop and think if this is really the best tool for the job, or if you should use something else instead.
There are special cases where it is possible, but it's not possible in general.