It might also be really useful to support syntax highlighting as I see one use-case for really quick and uncomplicated pair programming.
I built my own notepad a while ago too using ShareJS as the syncing library. (http://www.madpad.me/) https://github.com/sifxtreme/madpad
We did implement real-time collaborative editing for Teamemo (https://teamemo.com) and the real challenge was to support rich text editing.
Are there plans to support rich text?
I liked much more the workflow when a customer decided to use Google Docs for the technical documentation. We were editing and checking documents live with multiple cursors in the same screen.
I really† liked Hackpad as a wiki for my team; it was a lot easier to jot down thoughts and better followed the spirit of a wiki (from "quick" in Hawaiian), than the so-called "wikis" we see nowadays that are just bad CMS tools... I'm looking at you, Confluence.
†: enough to be a paying customer.