From my point of view it is a real usability issue.

zfs modules are not in the official repos. You either have to compile it on each machine or use unofficial repos, which is not exactly ideal and can break things if those repos are not up to date. And I guess it also needs some additional steps for secureboot setup on some distros?

I really want to try zfs because btrfs has some issues with RAID5 and RAID6 (it is not recommended so I don't use it) but I am not sure I want to risk the overall system stability, I would not want to end up in a situation where my machines don't boot and I have to fix it manually.