History of proposals to fix highway=path ambiguity – and a wayforward?

Definitely. See here: Adding T0/strolling to sac_scale

However that is not a safe assumption as long as we have paths that are difficult_alpine_hiking and your second picture sharing one tag :-D. I mean, I could definitely work with voting on such assumption and limiting pathto something narrower, but I am probably in a minority there :-).

I can imagine adopting notation like (inspired by Python but could be different)

sac_scale=demanding_mountain_hiking:alpine_hiking for T3 to T4 difficultyand sac_scale=alping_hiking: for at least alpine hking. Though I am notsure if it would make edit wars about precise classification less or more severe :-D.