Following below is attempt to reproduce sample described in https://www.phoronix.com/news/Archinstall-2.8.1-Released in virtual environment . To perform the testing first of all
# pacman -Sy archinstall [upgrade 2.8.0-2 => 2.8.1-1]
Then follow standard schema deploying Arch Linux Guest under KVM Hypervisor .
# archinstall
You may clearly see in the video https://www.youtube.com/watch?v=RJ6O0AglqQo&t=2s how to switch to testing been performed in the post above. Video itself is pretty nice, however, LVM feature evaluating was skipped in this video, regardless version of archinstall was upgraded to 2.8.1-1.
Per https://news.itsfoss.com/archinstall-lvm/
Then there are the plans to support encryption for LVMs across partitions, an option to manually configure LVM, and to deal with pre-mounted LVM volumes for the Pre-mount menu option.
References
https://www.phoronix.com/news/Archinstall-2.8.1-Released