Will Sweden's gender neutral pronoun "hen" be added to course?
It is in common use, though. It's not used /everywhere/, but many magazines and newspapers have started using it, and various other kinds of media. And personally, most of my friends have been using it for many years now. At first it does take some effort, as it often does when you add new vocabulary, especially in a category of words that most of the time stays the same way. But it's worth it.
The Swedish course on duolingo seemed quite gender-aware - "Hon" being used more often in examples then "Han", a hint at gay relationships, and men and women not sticking to stereotypical roles - which made me very happy at times and fits to the socially progressive image I had of Sweden.
You can say that "Hen" is not in 'common' uses, but it has been used for years in different communities, even in some magazines.
I'd embrace taking it into the vocabulary or at least mentioning it in the Tips and Tricks for pronouns.