After digging a little further, I see Brian backported the PATH modification support from issue #3561 in https://hg.python.org/cpython/rev/a9d34685ec47

This should probably be noted in the What's New document - while it's not technically part of PEP 477, that's still a good home for it in the What's New doc.

The lack of the Python launcher in Python 2 likely isn't a problem - at this point in history, switching between Python 2 and 3 is the most likely scenario, and in that situation, the launcher would have been installed together with the Python 3 installation.