If you're going to go to that much trouble, you might as well just compile Emacs to Javascript with enscripten and run it natively in the browser. The download time might be painful, but then we'd have a web editor actually worth using.
But why does everything need to run in the browser? You have a perfectly good OS and you can run Emacs natively and use tramp to open remote files over ssh. I do it every day, it's awesome because I'm using my local emacs configured the way I like it and I can edit files on any server that has sshd running. Problem solved.
It's even 24.1. I only have patchy wifi now so I haven't been able to finish the install yet on my tablet but it installed and ran M-x tetris just fine on my phone.
Sadly the vast majority of the C emacs core is platform-specific code, the sort of thing that emscripten would be worthless at.
That being said, a manual port of the VM and C modules is not inconceivable.