Do note however that there are more than a million highway=footway which explicitlyallows bicycles (via positive bicycle=* tag), and also dozen thousands of highway=footway which explicitly do allow non-bicycle vehicles (e.g. vehicle=*, motor_vehicle=*, motorcar=*, motorcycle=*, moped=*, mofa=* etc. with positive [not “no”] values).
On many of them, it is many cases intended that oneway=yes applies only to said vehicles, and not to pedestrians. However, in many it might apply to pedestrians too. Thus, the unwanted ambiguity (I hope we can all agree that ambiguity is bad?)
Without using extra tag or some other information, those are ambiguous: there is just no way to know what was meant by the specific mapper.
Same as with say ambiguity of sport=football – it might mean soccer, or it might mean American football. Depending on who you ask, it is “obvious” it means the former, or it is “obvious” it means the latter (with just a minority accepting the truth that without extra information it is ambiguous what is meant) . The obvious solution to address the ambiguity is to deprecate and not use that tag at all.
Unfortunately due to long time and huge usage, it is little too late to completely deprecate oneway=yes and replace it with combination oneway:vehicle=yes and oneway:foot=yes (as was done with sport=american_football / sport=soccer), so less intrusive solution is needed. One is suggested in that One-way for pedestrians proposal. It unfortunately isn’t as unambiguous as fully deprecating oneway tag, but it has an advantage that is significantly easier to implement.