I know that a few people have been using the Webmention and the Semantic Linkbacks plugins for WordPress together to show the backlinks in the “comments” section of their posts/pages. Perhaps this may work for your purposes?

A recent example I’ve seen someone put together on WordPress that does something similar (though not using Slippy) is https://cyberzettel.com/.

In a similar vein, though not with WordPress, Kevin Marks mocked up a UI for an incoming/outgoing links in the mode of a Memex that also leverages Webmentions for part of the functionality: https://www.kevinmarks.com/memex.html.

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