Idea: Encourage learners to write in the language they are learning via automated feedback messages based on context for their followers.
The idea is that feedback in a lesson or translation would come not just from Duolingo but also from messages that people you follow wrote that would be automatically generated based on context.
This context could include not only if you got something right or wrong but also the topic.
And so, when writing such messages for your followers, you could use Google like queries to target them towards various contexts.
Whenever such a message is to be generated, the system would take into account all candidate messages from people you are following that are applicable to the current context and would select one of them — possibly based on whether that message was well received in the past by others.
And of course, you would know which person wrote that message. If you don't like it, you could ask that you not see this message again or any message from that person again. If you like it, you could say so as well.
And the person who wrote the message would receive feedback in their stream whenever that message is generated that would include whether the message was well received if that information is available.