It doesn't replace the OS, but all of the "viable for developer" parts of it come from running inside the Ubuntu chroot, so the fact that ChromeOS still exists is mostly academic in this context.

FWIW, I've owned one of the Samsung ARM Chromebooks since the week it was released and I've been running crouton for a couple of months now and it works really, really, well. I still use the ChromeOS side for very simple browsing (the Aura window manager is nice if all you need is the web) but switch over to the ubuntu/X11 interface often to do development work.