Please check out the Facebook page and group dedicated to promoting a new Ancient Greek course for Duolingo.
If you'd be interested in helping develop this course, please apply on the Duolingo Incubator site: https://incubator.duolingo.com/
If you'd be interested in taking/trying the course, please follow the initiative on Facebook:
The Duolingo platform allows for several alternate forms, which could encompass a range of AG dialects (Attic & Koine). The Modern Greek course is a good litmus test for this.
Since the pronunciation question is likely to be controversial, I imagine releasing the course without audio (at first) will probably be the best approach. But we'll have to cross that bridge down the road, since this could take years to get off the ground.