Thanks for linking this, I would not have expected this usage (more from the iPad side being locked down) and it has inspired some thought.

It can be used to mirror content for offline viewing, e.g. share sheet sends URL to iOS shortcut, which uses SSH to send yt-dlp or wget archive command line to Linux sidecar, which has microSD storage (more capacity, lower cost/GB). Linux can host WebDAV/CalDAV and SFTP content for iPad apps and media players.