I really thought that 1.5x playback speed would be the same as 1.5x generation speed. Wow. Looks like I was wrong.
Regarding the subscription — I thought that no subscription was actually a competitive advantage, but now so many people are telling me to do it, that I'm really not sure anymore.
Did you try 1.5x generation speed and hear an improvement? Mine was totally just a guess. If it is better and you can beat traditional audio books on quality that would be cool. A lot of people listen at higher speeds.
Re:subscription - maybe try both and see? Assuming most people listen to the same books, your generation costs should plummet pretty quickly.
Pricing: maybe try a mobile app with monthly subscription? Something for recurring revenue.
Features: can you generate at 1.5x speed? Might be more natural than the playback speed up options and be a nice differentiator.