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.