[1]: https://squeak.org/
At this point, you can either copy over the difference or just replace the whole production application. I'm not sure which would be faster.
I don't think liveness is important for a production system. I prefer production to evolve in discrete chunks. Liveness makes sense for development.
I suppose one other benefit of a live system is that you could deploy an update without without restarting the application. But at some level, you would be restarting part of the application, and you are just shifting the update logic from the networking layer to the function call layer or object layer or whatever minimal layer of swappable component you can deploy.
Or is the Smalltalk idea that you never update your software?
At worst the user would have to rewrite their code from time to time.
As many comments note, the proposal of this post seems a disaster regarding reliablity/predictability.
So why should I get excited about the ability to live edit when it's held up as bad practice in one of the few areas it's possible.
Modfiying web apps from the browser seems to be a rare case, interestingly. I think there were a forays[1] made in that direction, but the need for external tools to shoe-horn a half-shod module system onto JS was the final straw for that. Never mind the convenience of some nigh-essential language features (SCSS, ES6).