Improving the voices
I've seen suggestions here that Duolingo add staff to record real voices instead of the computer generated voice that has problems like pronouncing We live as We /laiv/ and running words together oddly, but that seems a little costly to me. Given that this is a community sourced application, could the words and sentences eventually be recorded by volunteers in the community? I'd be willing to volunteer some time to this effort. You could have multiple kinds of accents and voices that way too. ( I grew up in Denver, Colorado, in a middle-class neighborhood, so my accent is pretty much what you'd hear from most American TV and radio broadcasts.)
Absolutely support. There could even be a voting system, like there is for comments, on which voices are the clearest, to help new learners find them. Or just put in a system to allow comments with sound, since that would also allow native speakers to comment on learners' pronunciation.