What's the split like these days between users of Guix the package manager running on some other distribution vs Guix the distribution? Is one noticably more popular than the other?
There are many users of Guix at research institutes who aren't running Guix System (i.e. the full system). But the difference between Guix and Guix System is pretty small; even with just Guix you get the "guix system" command, so you can build containers and VMs that run Guix System. You only can't benefit from full-system rollbacks and the integration of Guix system services.