Steem Chat and Discord are both for live chatting, and I think it's hard to make a Dapp for Live Chat due to the 3 second transaction delay, but I don't see what's stopping anyone from making a Steem-based Twitter @themarkymark.
The "comments" and "replies" categories should work fine (for a Steem-based Twitter).
RE: Introducing Steem Social a new real-time chat