I didn't either, and I'm running FreeNAS 9 on my server at home. I didn't realize FreeNAS 10 was such a huge improvement.
If you have custom jails, then you really don't need my advice :)
I've just migrated yesterday and managed to replace all my jails with Docker containers, although the road was a bit bumpy, at least when it comes to the containers UI which is buggy as hell currently.
All in all I'm delighted. The CLI is great, the UI buggy but definitely better, and no more jails but proper containers instead.
Congratulations to the team and thank you for delivering.