Perhaps part of the problem is that the wiki currently only shows well-behaved examples. If both casual mappers and data consumers were aware of the fact that both of the following paths:
 |
 |
| could be tagged like this (without necessarily violating the wiki): |
highway=path
foot=yes
bicycle=yes
surface=ground
mappers might become more inclined to also add smoothness tags and data consumers might become more careful when evaluating the access tags.
Yes and for example in Bavaria this ruleset changed less than 2 years ago and the wall of text describing it contains things like:
If there is a risk that travel on the path will loosen the soil surface, increasing the risk of soil loss and soil erotion on the path, the path is regularly unsuitable for travel by bicycles or other non-powered vehicles.
Width, gradient, curves and clarity are to be considered, also in connection with the frequentation of the path by other nature users.
The suitability of a path may also be limited to the time of day or certain periods of a day for reasons of community compatibility.
…
This applies, for example, to unpaved paths that lead across alpine pastures where there are animals. Particularly during the nighttime (between sunset and sunrise), entering these paths can trigger panic reactions in grazing animals, leading to injuries and damage.
In my opinion we should not even try to boil stuff like this down into foot=yes/no or bicycle=yes/no, because the correct answer in such cases will always be foot=maybe and bicycle=maybe, no matter how much we do not like it.