The linked post makes it pretty clear that this is NOT a production ready release. 9.10 continues to be the workhorse. Did they just want to reach a new milestone for the optics?
https://forums.freenas.org/index.php?threads/this-week-in-fr...
Renaming to 11.0 - As many of you know, we’ve been hard at work on what was to become 9.10.3 in the next few weeks. As part of this update, we have also bumped the base OS version to FreeBSD stable/11. This is a significant enough update that we wanted to take this opportunity to return to a saner form of versioning that more closely follows the underlying OS version. Moving forward you’ll be seeing releases like 11.0, 11.0-U1 (Update #1), 11.1 and so forth, eventually moving to 12.0 once we rebase on FreeBSD 12 (still a couple years off).
[0] Docs are a little spartan, but google searches got me up and running a virtualized linux image in less than 15 minutes. https://doc.freenas.org/9.10/jails.html#using-iohyve
That being said, I'm holding onto 9.10 for a few months, to see how this release turns out. Moving my jails to docker is a welcome change, but not something I want to jump on immediately.