x-callback-url deep linking support would open a universe of automation opportunities.
I could update my Alfred workflow to provide a global quick-open tool for example, or like my NotePlan Alfred workflow, it could create new pages in Joplin programatically.
Another huge thing it might accomodate is integration with Hook: Integration: How Hook Works with Your Favorite Apps ā Hook
It can be difficult to grok Hook at first, but it's "Copy Markdown Link" feature is easy to understand and demonstrates how incredibly powerful it is. You can create a concise URL to pretty much anything, files, emails, websites, etc. that you can open anywhere. With x-callback-url deep linking support in Joplin, I could use Hook to create a link to a Joplin page and paste it into any app, like my task manager of choice to schedule an action on a specific date. When the date floats up, I click the link, and it opens the page in Joplin. And visa versa, I could past a Hook link to a task into a Joplin page that links back the other way.
It's like an abstraction layer over the x-callback-url schema that hooks apps together without the need for any other form of scripting or automation.
(I have no affiliation with Hook by the way)