Earlier quoted context omitted.
An image bookmarking app that can suggest similar images is a genuinely useful thing. That allows a user to rapidly collate a set of images based on some theme (so for example I use it for design/illustration projects). Despite the UI, it works, and I can't think of any other apps that do the same thing and have a better UI, so :shrug:. However I'd still agree with you 100% on its cancerous nature: it's an app with a…
Wanna start one? There is an interesting overlap between submission of links (HN/Reddit/Lobster), bookmarking them (Del.icio.us), image based collections (Pinterest), and push-pull feeds (RSS/Feedreader).
I think the major hurdle is that the thing that makes it useful is an extremely large bank of images, and ability to share within the app. So that implies a social aspect, and then that needs to be gated off from search results
This has existed several times before -- this is very vague because I'd forgotten about until now, but the one I used to use in the early 2010s (?) was an invitation-only site with very simple UI, almost bare HTML (similar to pinboard), a weird name and a logo that was I think a gorilla. Used to have very high quality results, albeit highly focussed on art/design, with a small, dedicated user base
Edit: it was FFFFOUND!, shuttered in 2017 (Pinterest seems to have killed most of those sites, so how does one go about breaking that monopoly?)