The thing is, usually the legislations are not “On highway=cycleway you have to cycle in direction of the OSM-way” ( though that would be funny 
).
It’s more like, there is a law affecting in OSM-terms a random set of ways and a certain set of users. The ideal (easy for mappers to understand and add and clear to the data consumers) solution would be to discourage the usage of oneway on “paths” and only use it on “roads”. It seems on roads we all have similar understaning internally and as well the rules on roads are mainly based on signs and kind of globally of the same meaning. But on “paths” that’s not the case resulting in a rather random result for the data consumers.