Interesting note. I think that part of the problems arise when the implementation is partial, for example if you transclude a page that does not implement webmentions, etc.

I, for example, can receive webmentions but do not send them (yet), because I couldn’t find a good approach to implementing them in my static website builder.

I wonder what would happen if you start with a small, closed group of people, say colleagues in a company, research groups, etc. Perhaps an experiment at smaller scales gives an idea of what to do at larger ones