This is more of a "stop-gap" solution to bring the original proposal of using DMs as chats. "Chats 1.5" is more of an umbrella term for optimizing user experience in private conversations, i.e. DM threads with multiple people. This isn't limited to private conversations, however as same improvements can affect public conversations, i.e. displaying hellthreads as chats might be a good idea. Also doesn't necessarily have to be chat-like display, i.e. implementing virtual scroll for threads would also be part of this.