Sorry for being out of the loop on this thread the past several days. I was at a cartography conference. The organizers must have been thinking of all of you, because they chose to hold the conference at a hotel with this inviting-looking not-a-crossing directly in front. foot=no wheelchair=yes, I guess. 
But what is the inverse? Wheelchairs are legally allowed almost anywhere pedestrians are, but the law expects wheelchair users to know their limits. I have pretty much only ever seen wheelchair prohibition signs on escalators and the occasional steep incline, just in case. A narrow doorway never comes with a sign warning wheelchair users not to take out the doorpost when ramming through. Does that mean wheelchair=no should be nearly nonexistent in OSM?
The access restriction documentation recognizes that wheelchair and stroller users need information about physical suitability much more than they need to know where theyâre legally allowed. Why only them? Why not also recognize that the legal right to scale a fence on foot, or freestyle down a flight of steps on a bike, would be out of scope for a mapping project?
I donât think anyone is actually arguing for such extremes. So when we say that some mappers indicate suitability using access keys, letâs give them the benefit of the doubt too.
Thereâs a certain elegance to this approach, but it requires us to depart from the notion of highway=* as a thematic key, limiting it to things actually called highways.
By the way, the more poetic option would be byway=*, as in the phrase âhighways and bywaysâ. Others may know better, but I get the impression that a stereotypical British byway would be an obvious highway=path today, or at most a highway=track.
That said, moving paths from highway=* to byway=* would potentially cause two kinds of confusion. One is the British legal designation byway open to all traffic (BOAT). As I understand it, a BOAT could theoretically be any kind of road, track, or path, even a nonexistent way. BOATs are tagged designation=byway_open_to_all_traffic; we might have to educate mappers about the difference between a wayâs identity and its legal designation for the purpose of limiting access.
The other issue is that North American English seems to have all but forgotten the term byway, except in the names of heritage road routes, such as the Ohio River Scenic Byway, which goes over nothing but well-paved roads and even some stretches of freeway. Fortunately, speakers of these dialects are used to words like âtrailâ and âbywayâ clinging to more car-centric infrastructure.
Anyhow, even a more elegant byway=* key wouldnât solve any of the logistical obstacles that have been raised around pathway=*. I bring it up only as a curiosity, for completenessâ sake.