Reading up on it, recent releases of Ubuntu have dropped using ZFS for your boot and root volumes, which isn't ideal, however, they still support ZFS for any other volumes, which I'd venture is it's primary usage anyway, and they don't plan on removing support for anything other then zsys/zfs root/zfs boot.

But thanks for bringing this to my attention. I had missed the changes in 23.04.

There's been a recent series of PRs which appear to be adding ZFS root support to subiquity, the new Ubuntu installer:

https://github.com/canonical/subiquity/pull/1689

Cool, hopefully that means it's being kept as an option after all. :)