Bastille has merged support for bootstrapping end-of-life (EOL) FreeBSD releases as far back as 9.0-RELEASE. This extends support for legacy applications, testing and secure sandboxing for FreeBSD applications all the way back to 2012!
It goes without saying, any experimentation you do on ancient releases is your responsibility. We're excited to see what you do with this new feature, but please don't bring us the skeletal remains of years-old bugs in unsupported FreeBSD releases.
Bastille can import jails exported from iocage. We have a simple example here: https://bastille.readthedocs.io/en/latest/chapters/migration.html