This doesn't, necessarily, have anything to do with moving to SCALE.  Sure, SCALE apps are the intended replacement for plugins, but jails are quite a sound solution as well.  I've put a good bit of work into a script to install Nextcloud in a jail, and lots of people use that--I believe it's a solid solution.  You can manually install it in a jail.  There are good ways to get Nextcloud running on CORE--but the plugin isn't one of them.