> there would still be value in having a known reporting channel

Windows 10 has a "Feedback Hub" to report problems and search for existing feedback that's similar. You could report a problem with the "AppInstaller" app. In this case, the app execution alias targets "AppInstallerPythonRedirector.exe". This is a GUI program, so CMD won't wait on it and set %errorlevel% if run from an interactive prompt -- not unless one uses `start /w` to force it to wait. (Sidebar: CMD determines that it's a GUI program by querying the PEB address and reading the process PEB via ReadProcessMemory... hack-o-rama.) 

IMO, the installer-redirector in this case should be a console application that prints a message to stdout to inform the user that it's opening the store to install Python. If it fails, it should print an error message to stderr and return a non-zero exit status.