I'm reading a paper by J. Paolillo titled "Conversational" Codeswitching on Usenet and Internet Relay Chat" His description of Usenet and IRC totally qualifies as a futuristic killer of Twitter. But then you see the years of references and remember that these system predicted social media long time ago.
The rest of the article is great. I recommend it to everyone on the fediverse, not only to people who are interested in codeswitching. The article is available at http://www.languageatinternet.org/articles/2011/Paolillo The whole journal worth checking as well.
In my opinion, Facebook and Twitter took a step back by taking the moderator role away from their users and assigning it to algorithms, social network employees. Yes, you can hide things, so they are not shown to you, but that will not change the social norms in the community.
Mastodon and other ActivityPub implementations can shine in this respect by giving their users the tools not only to hide content but also expressing the social norms.
A beta setup of a Mastodon instance primary for family and friends.