@thomasboettnerMSIX is technically a user-based installation, if you double click the MSIX file this will register the application only on the user that installs it. However, all the files are placed in %ProgramFiles%\WindowsApps\PublisherName.AppName_AppVersion_architecture_hash
If another user wants to install the application, this will only register it on that current user.
All files (including user files) are present in the above location.
From some tests that i did, when you provision an app on all users using
Add-AppxProvisionedPackage -online -PackagePath "c:\package.msix", after another user logs in on the machine, the install (or publish to be more correct) of the app will happen silently and all the userdata that is present in the VFS of the MSIX (from %PF%\WindowsApps) will be published in the user location: