It seems to me that differences between countries are mainly due to differences in access tagging (which in turn reflects real world access differences), not the use of oneway itself. Germany has a lot of shared use footways so most oneway tags mean vehicle (bicycle) only. Some countries have hardly any instances of shared use footway, so fewer oneway tags on footway overall, but those that exist refer to pedestrians.
That’s what I saw in Ireland: shared footways are infrequent, but where they occur (tagged as bicycle=yes), oneway consistently refers to bicycles. While for normal footways it consistently refers to pedestrians. So no actual ambiguity, at least for highway=footway.
For that reason I’m not sure it makes sense to give much importance to countries, mentioned several times in your list. Regardless of the chosen approach, it seems documentation should focus on mapping specific situations, more than countries. (I note the highway=footway wiki makes no reference to how a oneway footway might be mapped: none of the possible oneway tags is listed as a “useful combination”) .