I am also working out something similar: a central “newshub” where all news (multilingual) is managed and a few “affiliate newssites” which list the news articles.
I’ve tackled the duplicate content issue by disabling a “public front end” on the newshub website AND by giving each news article a dedicated affiliate site.
The newshub site generates JSON feeds for each affiliated website which are then pulled from each affiliate site. The JSON file is then cached on the affiliate site which uses custom controllers and templates to render the news from the JSON file instead of from “kirby pages”. This works perfectly (and news articles can even be cached), but it also has other issues I haven’t found a solution for yet (e.g. make them findable via site search, or re-create the pagination object). If anyone has ideas and would like to discuss this, I’m all ears 
I also have a proof-of-concept working which “pings” the affiliate site upon each “create/edit” of a news article on the newshub site. That ping then busts the cache on the affiliate site and drags in the updated JSON. I can’t use that not yet though, because of a nasty bug with hooks in the panel.