I looked in the wiki and all over the various OpenZFS/ZFS web sites, and they all come from a UNIX perspective which I don't honestly care too much about (despite the fact I started with UNIX). One question which is important from a Mac perspective is if ZFS volumes support FileIDs.
Back in the day (System 7), files and folders on a Mac were referred to by volume and a 32bit value, not a file path. This means that things wouldn't break when moving or renaming files or folders, including aliases.
In case you come from a UNIX background, I'll clue you in on something: aliases are not symlinks or hard links. They are an arbitrary description on how to find a file, and on HFS filesystems could have the volume and ID of a file as opposed to merely the equivalent to a file path. On UFS filesystems they were basically symlinks which are fragile.
(for a long time Cocoa apps couldn't handle files being renamed or moved while open until they started using File IDs internally, although I don't think Apple ever exposed the mechanism in FoundationKit because they're idiots)
Anyway, this is a really nice human interface solution to a problem which won't be fully solved until someone develops an OS that doesn't have files to begin with, and I don't see any mass adoption of ZFS without such a feature.
I undertand that the HFS method for implementing this feature (a catalog file) may be impossible to achieve and the knee-jerk reaction to this may be to dismiss me completely based on that alone, but I would prefer a more constructive conversation than what I've typically experienced in open source projects.
I don't know enough specifics about ZFS to suggest an implementation method, but basically it's a file reference that isn't supposed to break unless the file is deleted. If you hard-link a file (assuming one would ever want to implement hard-links), each hard link has its own file ID in MacOS and behave much like a file path except they don't change.
I honestly don't care as much about case sensitivity, although it's nice to disallow similarly named files to avoid confusion (which I'm sure was the original intent).