It looks like FreeNAS is, eventually, going to run on top of Debian Linux, not just FreeBSD. VP of Engineering Kris Moore posted today:

[…] we’re going to be hard at work in 2020 to make our 12.0 code portable across multiple OS platforms. The middleware at the core of FreeNAS is already pretty portable today, and we want to start extending its reach.

That’s pretty cool. Good on them to unbolt their software from the underlying OS. I think it will give them a lot more flexibility going forward. I don’t know if I will run FreeNAS on Linux anytime soon, though. I learned to adore BSD’s stability and simplicity from running FreeNAS, but it has made it harder to virtualize and/or run some useful services on my hardware.

Kris Moore went on to clarify:

FreeNAS as it exists will continue on FreeBSD for 12.0 and beyond. This will be bringing some of the same software-base to Linux to unveil some new products that are Linux-based in the coming months. If you currently are happy with FreeNAS as it sits today, you can expect to keep updating it on BSD going forward.

All of this sounds good to me. FreeNAS has been a great platform for me for many years now.