Interesting that they're bringing Word Runner to Android first rather than iOS, not to mention the installed base of Fire HD6, which still hasn't gotten Fire OS5 update. I would rather they add TTS support (that would allow using Spritz, which would not have the 'only some books' restriction of Word Runner), but am looking forward to trying it out. Finally, typography free reading!
Update: in adding Word Runner, it seems Landscape orientation is no longer available on my phone. Conversely, on my tablet, Landscape is still there, but Word Runner switches it to Portrait (I rarely take it out of its landscape oriented dock, so that makes Word Runner unusable). Bookerly, yes, but apparently not yet 'enhanced typography'.