The File Filesystem (2021)

This is really neat, but when I saw the headline I got excited that it was something I have been looking for / considering writing, and I figure the comments here would be a good place to ask if something like this exists:

Is there a FUSE filesystem that runs in-memory (like tmpfs) while mounted, and then when dismounted it serializes to a single file on disk? The closest I can find are FUSE drivers that mount archive files, but then you don't get things like symlinks.

Not purely in-memory, but something like https://github.com/jrwwallis/qcow2fuse maybe? It's clunky compared to OSX's DMGs, but if you squint it achieves similar ends.

Otherwise you could achieve this with a tmpfs wrapped to serialize to a tarball (preserving symlinks) when unmounted.