So that’s just the kernel and it provides it’s own user land? Is that user land itself some a kind of app container host I could run Linux apps in for instance - but at arms length from each other? Am I getting this right?

guix-the-package-manager can be installed on any GNU/Linux distribution. It's a great way to access bleeding-edge software on a "stable" distro such as Debian or CentOS.

It has some nice properties such as not needing root privileges to install things, atomic upgrades and rollbacks, reproducible builds, multiple or transient (optionally containerized) "environments" (collections of packages), etc.

Guix System is a full distro built around the package manager. It gives you atomic upgrades and roll-backs for the entire system (you can choose any previous "generation" in the boot loader).

This sounds quite exciting. I could use this right away, with all the software I’m used to, and get all the benefits.

aside from the standard GNU utils right now it's mostly just guix the package manager and https://www.gnu.org/software/shepherd/

It's a whole GNU system distribution using Guix to build the system reproducibly, providing roll-backs at the system level, using Guile Scheme even as early as the initrd, etc. I don't know what you mean by "GNU utils", but "Guix System" is quite a bit more than just Shepherd and coreutils.

Ah lovely, as an alternative to systemd? Sweet!