I think the only thing holding me back from going for immutable Linux is desktop virtualisation. VirtualBox and VMware can't be installed on an immutable distro AFAIK, and libvirt isn't all there for Windows guests.
what issues have you had with libvirt and windows? Once you get the windows drivers installed, it works pretty much the same as other solutions. only thing thats still a pain in the ass still is shared folders.
Mainly GPU acceleration without passthrough from the last time I tested (Modern Windows is slow without it and passthrough might be an issue on immutable distros), but shared folders is something I use quite a bit on VMware. I remember trying virtiofs when I used passthrough, and it was suffering.