> Nobody else interprets the tag in that way.

The wiki is the canonical source of how tags are interpreted. There are multiple consumers and renderers of OSM data. They need a place to document and agree on how tags are interpreted. That’s the wiki. If a renderer like cyclOSM is going to deviate from what the wiki says, they’d better have a good reason for it — and engage with people on the wiki and other renderers to improve the tagging schema so it’s unambiguous.

You’ve probably not seen anyone else interpret the tag that way because there are very few renderers which cater for cycling. My guess would be that most renderers basically ignore the bicycle= tag.

> Cycle routing algorithms include "dismount" sections - so it is important not to use this tag for places where cycling is prohibited. 

I think this gets to the crux of this particular issue. Perhaps some additional tagging is needed to disambiguate between “this way is part of a cycle route but you have to dismount for a bit” and “this way is a footpath but connects to a cycle route so cyclists are reminded that now is the time to dismount”.

I think the distinction between highway=cycleway bicycle=dismount and highway=footway bicycle=dismount would be sufficient?

I don’t know why you’re talking about motorways, they’re obviously not relevant here.