Does developer mode come with a c/c++ compiler ? can you change the boot loader ? how about install a new shell ? replace the browser ? lets say you come up with a cool hack while in developer mode do you have to convince your friends to run in developer mode too ?
Chrome OS uses Gentoo's Portage package manager. So to install say, emacs, you simply do # emerge emacs, or whatever you want to install.
Anyhow, there's also plenty of online instructions on how to use Crouton to install Ubuntu onto Chrome OS, the point is that Chrome OS is a full, real Linux distro.
If it was endorsed by Google, you would have a user friendly way of doing that with full documentation, instead of hacks having to be explained by users via YouTube videos.
Advancing the web still makes sense.