Electron: Atom & App in one executable

Single executable isn't possible (edit: AFAIK) because several dll'slibraries, content_shell.pak and icudtl.dat need to be distributed with the executable.
You can fake it (on Windows) with an app like Enigma VirtualBox. This way you create a virtual filesystem inside a container exe. I wouldn't recommend it though, increased memory consumption for each atom.exe process.
edit: I'm assuming with 'Atom' you meant 'Atom-Shell' in this case.

Thanks for the explanation @bwin. I was just curious why it wasn't being done, I guess that answers it, platform support.

Yes I was talking about atom-shell, strangely the binary is called Atom.

The structure of Chromium is not designed for putting everything into an executable, and it would take too much effort to do that. So unless that situation in Chromium changed atom-shell won't support this.