Well, Emacs can’t really be an operating system because it doesn’t implement things like file systems, device drivers, and a TCP/IP stack. When we joke that Emacs is an OS, what we really mean is that it can replace many or most of the user-mode system utilities.
Remember that experiment that ran Emacs alone on a Linux kernel? That’s pretty close to Emacs as an OS but, really, who would want to work in such an environment? It was an interesting and revealing experiment but not really practical.
Now, Howard Abrams has come close to a practical Emacs OS. He configured Emacs to act as a window manager. Almost all of the action takes place in Emacs including shells and, through eww, most browser activity. For the occasional Web page that requires JavaScript or otherwise doesn’t render well in eww, Abrams arranged to pop up a Chrome page. Take a look at Abrams’ post for the details.
Although the system is clearly usable and useful, it’s not one that I’d want to live in. To be fair, it’s not one that Abrams lives in either. It’s the setup he uses for a virtual machine running on his work laptop that he uses for personal work. That way, he keeps work and personal computing strictly segregated. It’s a nice solution for that situation and one that you might want to explore if you have a similar problem.
I’m really comfortable in my highly customized laptop environment and so in a similar situation I’d shove my laptop into my backpack and take it with me. I will say, though, that as I move more and more of my work into Emacs, a setup like Abrams’ might be good enough for occasional work like personnel computing at work.