This could easily be implemented on top of any existing filesystem, why would it benefit to be implemented at the fs level? Versioning makes sense for performa

This could easily be implemented on top of any existing filesystem, why would it benefit to be implemented at the fs level? Versioning makes sense for performance but adding metadata sounds like a huge can of worms with no obvious benefits for a low level implementation IMHO. Besides your metadata wouldn't carry well to other filesystems (most USB drives still use FAT...) so it would be a bit of a headache to get right. Look at the mess that are file permissions and ACL already.