App extensibility is a priority for the first half of 2016. It will be different from the design patterns used in the Classic product’s Library and Reading SDK, but it will satisfy many of the same use cases. In fact, our goal is to deliver deeper, cross-platform extensibility than the Classic product allowed.
I really think that's a mistake in the documentation. I would give calling those APIs a try on Android and Windows, I can't imagine why I wouldn't have included that set in the list when we built the custom storefront/reading APIs for Android and Windows native viewers in DPS Classic.
Edit: Jamie corrected me, those APIs really are iOS only in classic.