Can you do those ad-hoc though? I was looking into this too. I feel like it requires a system config change, apply, and then you need to do container start + machinectl login to actually get a shell.
That's definitely what I want... most of the time.
* declarative mode, where your guest config is defined within your host config, or
* imperative mode, where your guest NixOS config is defined in a separate file. You can choose to reuse config between host and guest config files, of course.