It was part of the first beta release that the new iTunes wouldn't support XML exports. So there was warning that it wouldn't work. Public API's doesn't mean "something will never change". It should mean that API's won't change between minor version numbers. The entire purpose of semantic versioning is that there might be major breaking changing when there is a major release.

Apple did in fact provide a method to share music between apps and some apps do take advantage of it. Do you really think that Apple didn't need to do a major overhaul of iTunes?

Of course it's Apple's advice and common sense not to upgrade your OS until the apps you use are updated to support it.

This is all modern software engineering 101.

As a developer there are a few expectations.

- depending on private method may break your code with any point release. The vendor has no obligation not to break code if you depended on a private API.

- If your code breaks calling a public method during a point release, it is a bug and the vendor has an obligation not to break public API's when releasing a point release.

- If the vendor makes a breaking change during a major release (x.0.0). It's the vendor's responsible to communicate the breaking change and give enough notice to developers/users about breaking changes so that either the developer can fix their code, the user can find a replacement app, and/or the user not upgrade.