It would be great if Pipelines supported more operating systems than just Linux. It would give Travis-using developers a strong incentive to switch to BitBucket. FreeBSD, thanks to Jails, would probably be the easiest OS to add. There are several Jail managers available for FreeBSD, for example:
https://github.com/iocage/iocage a popular native Jail manager, using ZFS clones.
https://github.com/kvasdopil/docker/tree/freebsd-compat port of Docker to FreeBSD, using ZFS. It can also run some Linux images using Linux binary emulation
https://github.com/3ofcoins/jetpack An experimental implementation of the App Container Specification.