I’ll create a spec based on this so that at least we have something to go to if it ever gets implemented (I’d like to).
That's great to hear, thanks for taking this on board Laurent.
For the Zettelkasten method, isn’t it just about adding support for back-links, or is there more to it?
That's the gist of it yes! Essentially it would allow users to use Joplin like a Knowledge Base. It's arguably a superior way to organize ideas without worrying too much about directory structure (and losing notes buried deep into sub-notebooks).
As @roman_r_m mentioned it would be really helpful to have some autocomplete feature when creating bidirectional links. In Zettlr, when you type "[[", it prompts you with a drop down menu with autocomplete by note title. So for example typing "[[shop" would automatically show you the note named "shopping list", then clicking enter would create the bidirectional link [[shopping list]].
There is one more advanced feature implemented in some Zettelkasten-compatible software, which is the ability to view one's note structure as a graph where each node is a note, and each connection is a bidirectional link. For example, Roam Research and Obsidian both emphasize this feature. But I personally think this should definitely not be a priority: bidirectional linking is they key to an effective Zettelkasten workflow, the graph is bonus but not essential.