Give people a place to come together and see all the interesting conversations going on in the Write.as community. From here, they should be able to find an interesting conversation (i.e. blog post) they might want to jump into.
This is where Remark.as starts.
Call it something grounded in real life, like the "Café" (sorta like midnight.pub's pub metaphor). List 50 or so most recent posts from everyone who's opted in to showing their posts here.
Clicking a post takes you to the post, with a place to respond (T879).
Center Stage? Give people a shared space they can alter, that everyone will see. Kind of like a chat room "topic" but with the ability to share multimedia. Maybe they want to share a song they're listening to, or a funny video. Maybe it'll be a question. Limit the message length, make it clear that it affects everyone, and see what happens.
Chat. Give people a way to talk to each other and shoot the shit outside of blogging.