Was the point that memoryview.tobytes() has a known data corruption bug in 3.2 and 2.7 raised in the previous discussion? I'm pretty sure I had forgotten about it, and I don't remember it coming up in the thread.

The trickiest aspect of a backport of the new implementation is that we need to preserve the C ABI - extensions compiled against any maintenance release should work with all maintenance releases in that series.

The new APIs aren't a major problem - just sprinkle a few underscores around to mark them as private on the older versions (I've certainly done that before when a bug fix genuinely needed something that qualified as a new feature: implemented a private version to use in fixing the bug on the maintenance branch, then promote that to a public API on trunk)