I have not had a chance to thing through this much but here are some observations that are tied to the fact that currently we have 1:1 mapping for resource → url while in practice it's more of 1:n mapping because:

1. HTTP redirects.
2. Hash in URL still points to same resource.
3. Moving / renaming files on disk leads to multiple results for the same resource.
4. Some links on the web point to HTTP addresses, but navigating to them upgrades to HTTPS. Result is we don't recognize siblinks (same problem as HTTP Redirect).
5. My markdown note appears as local file, published on github it has different URL, if I also publish to static site it has yet another URL. Would be great to recognize those connections.
6. Any content on IPFS can be accessed through arbitrary gateway URLs will be different but resource would be the same.