If they still call the executable "python" then they’re demonstrating the whole issue with keeping the same name for wildly-incompatible upgrades: it “shouldn’t" matter what version a reasonably-modern OS chooses and yet it does, solely because of the name. No one would complain about having "/usr/bin/python", "/usr/bin/py3k", "/usr/bin/perl" and "/usr/bin/rakudo" all at once on the same OS but being forced to choose two is insane.

So like, the same thing that happened between various perl versions (inc 4x -> 5x) and python? Or C++ versions? or even c-library or executable format changes?

Things break sometimes.