Thanks for your revisions. Hopefully we can keep the community focused on constructive approaches to solving these problems – a “third way”, rather than a third rail. 
Ah, maybe I’m reading too much into the proposal’s tagging instructions regarding crossing:saltire=*. If I understand correctly, the primary issue is that routine conflict points within a street or pedestrian plaza are tagged as a kind of crossing, so the bits about crossing:saltire=* are somewhat distracting. I’d suggest devoting more space to explaining the concept of a conflict point and contrasting it with a bona fide crossing. The explanation can mention crossing:saltire=*, among other things. I’d also suggest removing the passage about implied protection systems or relegating it to a footnote, because it risks unintended future consequences in regions where it’s inaccurate.
Regarding bona fide crossings, navigation applications are already behaving more or less as they should by alerting the user about railway=level_crossing and railway=crossing and nothing else. If validators would simply guide mappers to use these tags more judiciously, then no algorithmic change would be necessary. Routers wouldn’t need to consult crossing:saltire=* or even the tags on the crossing railway. (The latter could be impractical, bordering on infeasible for some routing engines. You bring up StreetComplete as precedent, but it isn’t a routing engine – it doesn’t need to transform OSM wholesale into a routing graph or perform map matching.)