There's actually a really interesting article/email I read a long time ago saying that emacs main competitor was the browser, and that it was likely to be overtaken by it unless emacs reacted in some way.
I can't find the article with a cursory google search right now, but maybe someone else knows it can find it.
Scroll down a bit to the heading "The bad news: the competition isn't the IDEs"
"IDEs are draining users away, but it's not the classic fat-client IDEs that are ultimately going to kill Emacs. It's the browsers. They have all the power of a fat-client platform and all the flexibility of a dynamic system. I said earlier that Firefox wants to be Emacs. It should be obvious that Emacs also wants to be Firefox. Each has what the other lacks, and together they're pretty damn close to the ultimate software package.
"
Yup, that's it! Thank you. I love being able to tap into collective memory :)
It strikes me as true though, step by step we're moving functionality to the browser. In some ways it feels great, but in others it's terrifying - the thought of this (and the next) generation poorly re-implementing emacs in the browser...
I can't find the article with a cursory google search right now, but maybe someone else knows it can find it.