Ancient Language Courses - Latin, Greek, Hebrew
The benefits of learning modern languages is obvious. In an increasingly global culture, it makes sense (besides, we American's are to lazy when it comes to learning languages anyway).
I'd like to see Duolingo tackle some ancient languages: Latin; ancient Greek (Attic would probably be the most useful); Biblical Hebrew. I've learned these languages the traditional way, but I've been able to learn French much faster with Duolingo.
Learning ancient languages not only allows the wisdom of the past to maintain a presence in the modern culture, but it's extremely important to the academic community (historians, philosophers, etc...). If Duolingo were to launch ancient language courses, they would go a long way towards educating people everywhere in a way that would be both magnificently significant, but unique.
I like ancient languages, but I am really doubtful about them on Duolingo. However, Duolingo tends to privilege translation, which is the (only?) skill you need for them.
Nevertheless, I still believe that you need a solid background in the grammar of your target language, in order to read ancient writings. So, I am not sure. I don't believe a Duolingo course will be useful if done with the "standard" Duolingo approach.