Found this Janki plugin from this Reddit thread during research on spaced repetition. It says it "provides an Anki editor within the Joplin environment, allowing bidirectional links between your notes and your Anki cards."
Would this be useful enough to anyone that they'd want the developer to officially publish it?
As for alternatives, the Joplin Anki Sync plugin is officially published. However, the developer wrote that it may be too rough for others to use currently. Baeuda also exists as a Python project that converts Markdown files into Anki assets.
Are there any other spaced repetition plugins and apps that somehow interface with Joplin?
Are there any other spaced repetition systems besides Anki (like Supermemo, Mnemosyne, etc.) that you would like to use with Joplin?