It made me think of the pain in the Lua community in migrating from 5.1 to 5.3. I recently
I agree with your summary that Python's transition needed help from the core python developers, and I think it might be worth teasing out the two specific changes that helped increase traction in my interpretation of his talk:
* Backporting newer features into 2.x
* Emitting runtime deprecation warnings
As Victor said, these let people migrate over time - they could get their codebase into a state where it works with Python 3.x, while still using 2.x so there is no single painful migration.
I don't know if Lua has any more breaking changes in its future (and it would be nice to know, maybe if the development happened more in the open like a proper open source community project :) but perhaps these two aspects could be considered if there are any such changes coming :)