These are basic POSIX features, but I think the high-level point that Kurt is trying to make is that building a FUSE file system signs you up for a nearly unlimited amount of compatibility work (if you want to support most applications) whereas their approach (just do a loopback ext4 fs into a large file) avoids a lot of those problems.

My expectations are that in 2026 we will see more and more developers attempt to build custom FUSE file systems and then run into the long tail of compatibility pain.