As far as I could figure out so far, it looks like bcvk relies on sshd being enabled and started by default in the container image when trying to create disk images from it.
We should be able to dynamically enable the sshd service via a kernel parameter: https://www.freedesktop.org/software/systemd/man/latest/kernel-command-line.html
Likely systemd.wants=sshd.service.