This is a good hack, and it works better than a lot of alternatives, albeit Linux-on-Linux VMs have arguably few uses since systemd-nspawn exists (so you can just --bind the Pipewire socket in the VM)
I'd say that Docker has replaced more Linux-on-Linux VMs than has systemd-nspawn. That said, I'm seriously interested in what GP is doing that he's forwarding audio. Maybe testing desktop distros? Circumventing DRM? Multiseating an office with thinclients?
Docker is fine and dandy, but sometimes you just need to run an Ubuntu container that has to be persistent to run a few tests. debootstrap + systemd-nspawn -bD is amazing at that.
I am also curious about why GP needs audio in Linux VMs - I did similar tricks too but with Windows VMs, in order to pass-through my microphone to shoddy Windows-only corporate chat apps, but I never had the same necessity under Linux to be honest.
>I am also curious about why GP needs audio in Linux VMs
$dayjob requires an Ubuntu installation with certain security characteristics and certain software installed. And I'm not going to install Ubuntu or do any of those other things to my actual machines :)
I also have a Docker container (well, podman container) of Ubuntu, for running closed-source applications like Discord and Steam. For that one I do indeed just volume-mount the PA socket instead of ssh-forwarding it.