I just marked the associated PR as "[PEP required]", as while I'm in favour of merging this, I think we should go through the PEP process first:

1. We've been burned before by not properly advertising changes to Python's command line behaviour (while zip archive execution was added back in 2.6, a lot of folks didn't learn about it until the addition of the better advertised zipapp utility module in 3.5)
2. We should discuss the approach with the Cython developers and make sure that they're willing and able to support it when targeting 3.7+ before merging the implementation

Such a PEP will also provide a common answer to Terry's question above, as the "This allows Cython to be used directly on __main__ modules" benefit isn't going to be readily apparent to folks that aren't already familiar with the details of how Cython works.