Yep, it misses the selection of a language when writing a post, don't forget that some authors write in more than one language (native and English) making it more difficult for the usage of automatic language detection.
Peakd uses plausible and Ecency use matomo which can give you some interesting metrics (clicks, views, duration, retention...) ;) I think a good starting point for your project is an open discussion with major HIVE frontend owners. The hivesearcher (synchronises hivemind's posts & comments to an elasticsearch index) maybe also something interesting to help you in your project?
The red line exists only if the users don't know and don't agree about it but if you can separate those who don't want and use tools that protect the privacy of the others I think you will receive a good adoption.
Thanks for the links, that's very helpful!
Keeping users in the know about what they share and what not is one of my main priorities.