I am other users are already feeling the narrowing of options for where we can host our Joplin data. Webdav is an established protocol but it is very problematic and slow.
For the long term health of the Joplin project it would be good to see other cloud platform native support (see the rclone project for inspiration). This will open up Joplin for new users as well. Not every user can host their own nextcloud server instance to support a notetaking app.
This would be a good project for Google summer of code students as I imagine that working with APIs is something Google employees do often so good experience for the students.