Amazon is Honey Badger when it comes to the developer community. They don’t care because they’ve created their own tool set, their own ecosystem, and it’s working for their business plan/requirements.
It’s likely that they will continue to add new features like page “riffling” that will have a direct effect on layout and typography in the future. But they’ll do it in house and there will be no announcement to the world.
Bottom line: if you want to work in ebook production, focus on the companies that will work with you and the things that you can control. No point in driving yourself nuts over something like Amazon.
My biggest pet peeve these days: apparently no one tested side-loaded books on iPhones in iBooks in the last eon. iBooks + iPhone 7+ is broken as all get out. Wonky margins, highlights that aren’t translucent and cover the content are just the beginning.
The industry has moved past the time of “there will be multiple reading apps that just work with EPUB.” Companies have decided that not having some sort of proprietary skin in the game just doesn’t make sense because they need something to provide a strategic reason for customers to choose them over the competitors. Everything else should be considered a reference implementation. The Amazons, Apples, Kobos, and Nooks of the world consider it a concession to publishers to accept a most basic EPUB that will work across the board. Don’t ask for anything beyond that.
Hard, cold, truth. But then I’ve been watching this industry since 1996, so I have a pretty good history to look back on with hindsight that brought me to my current perspective.