tbh, databases of any kind could be used to make a chat application if your query structures are well setup etc.,. But the feature you are mentioning like havi

tbh, databases of any kind could be used to make a chat application if your query structures are well setup etc.,. But the feature you are mentioning like having threads could be easily be solved using like a document store ex; mongodb or any other no-sql db that could help you save time in both setting up things and querying. Just my 10 cents.