I looked into this for a project a couple of years ago (to boot VMs from minimal customized ISO) and ended up using mfsbsd instead.
I'm not able to find a lot of documentation on it. How does it compare to NanoBSD (and why did you choose it over Nano)?
For my purposes I needed an application server that would reboot to a known-good state, so I embedded the application code inside a mfsbsd live CD.