I've run into several applications that have child processes that when packaged in MSIX will cause the child process to break out of the container and then fail.
This is rather inconvenient as it's not normally obvious that some features of an app aren't working when they rely on a child process for the functionality.
This can be worked around with a wrapper script/exe that executes the main process with invoke-commandindesktop -preventbreakaway but it would be ideal if you could simply define the breakaway behavior in the app manifest.