The idea is that there won't be large amounts of backwards incompatibility in a single version bump. We all know how well that worked out for Python 2 -> Python

The idea is that there won't be large amounts of backwards incompatibility in a single version bump. We all know how well that worked out for Python 2 -> Python 3. There will of course be backwards incompatible changes introduced through a normal deprecation cycle. No one is suggesting Python remain static forever.