We agree on the principles. What we don’t agree on is if the adherence to such principles can come at the expense of the image visualization.
We have to accept that we are not in control of what data users are doing, and to some degree this limits us on the changes we can do to avoid breaking their functionality. If this requires us to tolerate minimal inconsistencies, then so be it.
Unfortunately, having both image and wikimedia_commons pointing to the same image results in OsmAnd displaying duplicate images.
Anyway, as the main problem is the visualization of guideposts in Waymarkedtrails, another possible solution is to limit the use of image keys pointing to Wikimedia Common files only for information=guidepost nodes. All the other image keys can be converted to wikimedia_commons.
This really limits the inconsistency to the minimum necessary.
What do you and others think?