Correction to point 3: I wrote "nobody fills that gap yet" before checking, and that's wrong. Web links have their own event type, NIP-B0 web bookmarks (kind 39701). On the same 6 relays over the last 7 days there were 146 of them from 19 authors (control with an impossible author: 0). Amethyst and Deepmarks are among the clients that tag them.
So the tool exists. What's missing is usage: 19 people against 695 with a note bookmark list. Building on 39701 (a better reader or importer) beats starting a new format.