On 16.04 the package names are different from debian 9 and selinux-relabel is not available at all in libguestfs - which means no support for VMs with SELinux based systems
fast-vm is available for Ubuntu 18.04 LTS and 20.04 LTS from version 1.7. Packages are provided directly from github releases instead of PPA which may be added in future.
With Debian packages it should be possible to run fast-vm also on Ubuntu. TODO:
Issues so far: