For tmux, that opens up pretty much any terminal based editor (vim, emacs, nano) along with all the extensions you might install with it (and the build environm

For tmux, that opens up pretty much any terminal based editor (vim, emacs, nano) along with all the extensions you might install with it (and the build environment). But for a protocol, I think what EtherPad (and google wave) had done with cell by cell action is what's needed. If google wave had taken off (and actually implemented their federation concept), I could definitely see people creating plugins to send and receive character operations via a google wave server.