Theia (and GitPod.io) will give you this today and it is compelling. GitPod gives you a single button on PRs/Issues that drops you in a dev environment, ready to build and test at the click of a button. No cloning, no installing a toolchain, etc.
If Rust and Rust Language Server are running in a container with Theia, this means I can use a Chromebook-style device for serious, real development without having to enable dev mode or even Linux apps. Every machine in the world becomes a real potential development environment.
Theia even has (or is about to have) debug protocol support too. A real, full IDE running on a remote DC, accessible from your browser. ( If you follow what the Theia and Che devs are doing, they're trying to support the full VS Code API... Which is SUPER exciting!)
(Note, with the level I'm speaking about here, the CRDT is a bit of an implementation detail, but it's useful for collaborative editing and in xrays case, syncing state b/w the browser client and the backend and the underlying SCM system.)
The expectations of advanced text editors have expanded to create performance concerns which do not apply to the most basic text editor. It's basically what happens when somebody tries to elevate a vulgar art by doing it big: like making the world's largest macaroni sculpture, anything can be done big enough to meet limitations. In addition to this, Atom also has the problems of being an Electron app.
Coordinating multiple editors is tricky, yes, but it doesn’t need fast hardware, just good software and ideally a reliable network.
Editing text on a phone is hard, but that’s a UI problem -- it’s the small screen and lack of a keyboard. Most phones these days have very capable CPUs and plenty of memory.
(I agree that this technology is very cool, though! I’m just curious why you pick out that low-end use case.)