I think making a change like this warrants a major version bump. It won't eliminate all the surprise for everyone, and I do have sympathy for the people who did go out of their way to talk about this on the mailing list and then surprised everyone. But it's common to pin yourself to a minor or maintenance release line to automatically pick up security fixes, etc. I expect breakage when changing the major (or even minor), and that's almost always a manual upgrade. And that's when I do read all the release notes, run tests, etc. before committing to the change.