Well, then let's make sure we specified what we'd like;) Here are some ideas for functional spec.
The service associated with an application package should not impact other application packages that use the same service - i.e. the service should be running within the container. The service should only be run when the containerized app is running.
It should be possible to handle multi-user operating systems (RDS or Multi-user Windows 10) and have different users run the same app and service in separate containers without interference.
Ideally this is handled by the MSIX Runtime. However, given the current runtime design of MSIX, this might mean requiring the PSF, possibly handled directly by PsfLauncher or via the new scripts (but I'm thinking PsfLauncher is better.
As Microsoft always love to have an app to associate with the requirements, let me suggest Autodesk AutoCad.