> Clearly it's not
What is your basis for this claim?
I am not an expert on this topic, but Gorhill is and has a demonstrated history of technical/privacy judgement.
Gorhill's comment makes it clear that impacting the functionality of blockers is an intentional change, as the proposal not only removes previous functionality, but also enshrines one particular and limited approach to blocking.
Edit: I would also note that "break" may suggest the possibility of altering blocking extensions such that they could keep working and maintain their present functionality. Gorhill's comment makes it clear that this is not the case.