You cannot simply copy your present jails over, you will need to create new jails and install new software in the jails. You may be able to use an old configuration file for whatever program you are putting into the new jail but not copy the entire jail.
I have not used any plugins but have used the jails. My Plex jail transferred fine from 9.10.2 and I have created several jails to help other troubleshoot. I can't say iv'e done extensive work with the jails though in FreeNAS 11, buit it does seem fine.
So to re-itterate: I would do like you are, create a new jail dataset, change your jails mount point to the new dataset, create you new jails and install the software you desire. If there are any files in the old jails then you should copy those over using the cp
command line or some other means. If you are storing data within a jail, you should try to stop that and store data in a seperate dataset. Example: You are downloading TV shows and you need to ensure they are stored outside the jail. Some folks have done it wrong and when they delete a jail, all the data goes away too.
Once you have your system running properly (not a second before) then you can destroy the old jail dataset.
Good Luck!