With v256 vmspawn is relatively complete now. For example it now registers with machinectl, also supports credentials, sd_notify, and so much more.
At this point, for my daily work it's now as trivial to boot a relatively fully featured VM (with TPM, SecureBoot, and all that fancy new-fangled stuff) as it is to to run a full OS container, and all I have to do is replace "n" by "vm" in the command line I use.
We also started to switch over much of systemd's test suite to use vmspawn.