I think whenever the Duolingo owl interrupts a lesson with a motivational quote (or the loading screen pops up for a slow data network) there could be small actual language facts.
My language is Japanese so if the owl came up, he could say something like, "San is the safe suffix for everyone you meet!" or in Korean as well, "Korean's characters are all variations of the same base characters!"
Duolingo doesn't really explain certain aspects of language like colloquial uses, short-cuts, or manners so I think it would be a big help to people who have no other way to figure it out themselves. I take classes in high school, college courses, and other apps for Japanese and Korean which is the only way I ever found these things out even after I used Duolingo for so long.
Pronunciations, charts, and writing exercises like Drops would help too! Even for small things like accents (for those of us who never quite learned how they work) would make a big difference.