Thanks for taking the trouble to write all this (when all I asked for was a link). It gives a good flavor of what you're talking about. I used to read network news inside of emacs, using a mode called gnus, decades ago, and before I switched to vim. That's probably an example of a complex application that could be written within emacs because of the architecture that you describe. This extensibility is tempting me to try emacs again, because vim is so hard to extend, but I don't want to give up vim's pure editing efficiency. I guess I need to see how well evil (vim mode for emacs) works in practice.