> This seems like the same fallacy of python’s 2to3, and why they should have written 3to2 instead.

This is incredibly insightful. I'm frankly a bit stunned. I would never have thought of this (and clearly the Python people also didn't) but it is absolutely true. It's also a very transferable strategy for any time compatibility is to be broken.

Is this an original thought of yours or do you have references to further reading?