'guix environment --container' allows one or more applications to be put into a container and you can optionally share files/directories from the host system with it. The distro built on Guix, GuixSD, has preliminary support for full-system containers using the same code that 'guix environment' uses. So you can have it whichever way you'd like.
It's init + your app, which is exactly what you want. PID 1 has some important responsibilities that aren't handled anywhere else. I'd argue that most init systems go far beyond what you actually want PID 1 to do, but that is a different discussion.
I definitely don't want any init in the container. I want the app runnning in there and nothing else. For a single application system, pid 1 has only 1 responsibility - collect zombies. I treat that as an emergency solution - apps should clean their children themselves under normal circumstances.
Everything else can be handled outside of the container.
https://www.gnu.org/software/guix/manual/html_node/Invoking-...