ZFS is several years old now. I'd think someone could implement a filesystem that borrows many of ZFS's best concepts and adds significant improvement. I haven't kept a very close eye on btrfs but I hope it meets this since it seems poised to take over as the new default filesystem in the next few years.
in the case of file systems, 'improving' around the original design decisions is often impossible. take hfs+ for example: almost all the filesystem metadata is stored in a single b-tree called the catalog. doing almost anything with an hfs+ volume requires exclusive access to the catalog, which locks out all other callers for the duration of the file operation. the solution is to spread the metadata out to other parts of the disk, but that can't be done without breaking hfs+ compatibility.
