I would like that Duo adds a tool in which one has to make a "writting" (letter, email, etc. ..) with a topic .. wich have to be correct by someone who knows the language (Lingots can be given to encourage them to edit), generating a great feedback for progress.
Me gustaría que agregaran una herramienta en la cual te den para hacer un "escrito" (carta, email, etc..) con un tema.. y que este, sea corregido por alguien nativo del lenguaje que este predispuesto a la corrección (se le pueden dar lingots para alentarlos a corregir); generando un gran feedback para lograr avances en el aprendizaje.
I would suggest using Lang-8 for this. It's a really good website and you have natives, and people that know the language correcting what you write and sometimes explaining what went wrong.
I don't think that Duolingo is a website that would work to cater towards this but you never know, right? :)