Firefox is implementing WebMidi so I don't think this idea people are passing around that these are "not real standards" so won't be implemented holds much water.
I was responding to WebUSB, and tacked a few other hardware APIs there. Both Firefox and Safari view them as harmful in their current form. They are not really on a standards track for now, they are "Draft Community Reports" or somesuch.
For something to become a standard that something needs two independent implementations. Before that it's just some browser's prototyping stage, no matter how many times Chrome will tell you otherwise.
Just three years ago Firefox's position was also largely negative due to unresolved security issues: https://github.com/mozilla/standards-positions/issues/58 It's possible those issues are now resolved, that's why it's making its way into Firefox. This means that Safari's stance may also change.
Same goes for other hardware APIs: from the point of view of both Safari and Firefox those specs have security and privacy holes the size of Jupiter. Not to mention that the quality of some of these so-called specs is very low. If/When these issues are resolved, we may see them implemented in these browsers, too.
Neither Safari nor Firefox are going to implement them.