Also see https://www.gentoo.org/

Or a linux that actually uses the BSD coreutils https://chimera-linux.org/.

Does it make ZFS on root stupid easy and has ZFS boot environments?

Alpine does. Just boot from the extended ISO and modprobe zfs and install zfs tools.

The normal, systemd NixOS does actually make it "stupid easy". It will fetch the latest kernel that is compatible with ZFS and has single-line config options for auto-snapshots, and the like.

Did not know this. Very cool. Does it also make it easy to replace grub with zfsboot environments?

I don't have personal experience with zfsboot - I have used UEFI/systemd-boot previously with ZFS root, and now use an initrd which loads the encryption key to ZFS root.

But NixOS itself does something similar, it has generations and if you change some setting and rebuild your system, the previous' link will be available in the boot menu, so you can easily try out stuff and just revert if it doesn't work - it is file system independent, but it only handles nix-specific stuff.

I am struggling to get systemd to cooperate with a TPM on boot right now, let alone ZFS. I'll probably drop back to initrd.

I just want encryption at rest for when it comes time to dispose of the disk, there's not supposed to be unencrypted sensitive data on it anyway.

Nope.

Void generally plays well with ZFS, including kernel updates, but installing on ZFS root is very much a DIY process.

Is the XBPS thing kinda like BSD ports?

Not really, no. It's just binary package system, ala apt or apk or whatever.

kinda. https://github.com/void-linux/void-packages/

Better yet just use Alpine IMO.