Here's a link on how to add it to different OS'ses but as said on another post I would not do that.
https://vdr.one/app-volumes-4-0-app-stack-os-mount-hacking/
That being said. You can still have multiple applications within 1 package and call the application Base.
The reason why I would not suggest doing this in Appvolumes 4.0 (and the reason why i really like the way it is setup now with 4.0) is that if you do have multiple applications (let's say 20) and you only need to change one you would need to change the entire appstack which could cause other applications not to work. Apart from that maybe someone wants to have a different version of one of those specific applications. you would need to create multiple appstacks to provide everyone with their specific version. Let alone testing the entire appstack every time even though you only update 1 application.
Still. At the end it depends on what you are trying to achieve with Appvolumes and DEM i guess and whichever suites your needs best. I do think that in the end the 2 version will disappear.