Just noticed that Tidal already implement a similar feature for albums and tracks.
Admittedly creating a sharable playlist that, similar to above, is usable outside of Roon is slightly tricker as the playlist first needs to exist or else be created on the fly.
One way to handle this is for the share.roon.com page to ask the recipient or viewer to login with their Spotify, Tidal, Qobuz or Apple credentials if they wanted to import the playlist.
It’s then just a couple of API calls (using the Spotify / Tidal / Apple Music API) to create a local copy of the playlist in their preferred platform and add the already matched playlist track IDs for that platform (see above) to it.
Going the other way and importing a sharable playlist back into Roon itself, Roon as I understand holds a snapshot of the Qobuz and Tidal databases, so in combination with the ‘playlist improver’ functionality, it should be perfectly possible to import a playlist from a share.roon.com link (or even a Qobuz / Tidal playlist link for that matter) using ‘best guesses’ from whichever of those services you are subscribed to.
In short, there is plenty of scope here for improvement, both in terms of sharing tracks / albums / playlists publicly and conversely importing shared playlists back into Roon.