NOTE: To be honest, I'm proposing this wild idea to feel out whether it would be well received. If so, I'm debating assigning some of my staff to this task down the line, simply because this would be useful for us. Chances are, this would wind up "wishlist" if anything, and rightly so. :)
This would be an app that could be used for real-time collaborative editing, much like Google Docs or AbiCollab. Async collaboration is throughout Phabricator, but there are real benefits to sync collaboration. In its simplest form, this would provide synchronous text editing, perhaps storing in Phriction.
However, it could theoretically be further extended to support the OpenDocument formats, thus allowing for both sync and async viewing and editing of uploaded documents - useful for those tasks that Phriction is not appropriate for. By that token, it could also be used as a means of better organizing Files, if one wanted to take it down that route.
Again, just feeling the idea out. If this were accepted, I might be able to put a couple of my programmers on it later this year (depending on our own project statuses).