I’m not sure what to do with these, because it’s sort of hitting the point of diminishing returns. As you said, there are a lot of possible marketplaces that could be added, and each one of them takes time upfront to implement, in addition to time spent maintaining them when their websites change. As much as I’d like to implement support for every possible website, it’s probably better to limit the scope somehow to avoid ending up with an unmaintainable or unmaintained mess, especially since we can input image URLs directly. I’m not quite sure what the cutoff would be, though.
I’ve also been thinking about a sort of “generic” provider that would try to extract the image(s) from any webpage using some heuristics. But as I commented in that thread, I’m not sure whether that’s a good idea either.