Should be doable with overlayfs (or similar) or alternatively some extensions to sqlar. sqlar is after all only a table definition, if you don't need FUSE acce

Should be doable with overlayfs (or similar) or alternatively some extensions to sqlar. sqlar is after all only a table definition, if you don't need FUSE access or are willing to write your own, SQLite3 can go a long way of providing arbitrary neat functionality.