I'm a bit curious if this could be bent into being a pair-programming tool. One of the core functions is simply routing multiple connected keyboards/mice to multiple concurrent copies of a given piece of software.
For example, in the way I was originally imagining it, you and me would sit down at a computer and I’d open the editor and we’d make concurrent edits. But then when I want to scroll, the suddenly you would not be able to scroll. And another example, if you were pointing and clicking at something, say for example that you were drawing a painting in Photoshop, and I try to move another window from one side of the screen to the other and suddenly I am occluding your window, and on top of that you might click in my window.
This was a few years ago so I was imagining a situation where both people were sharing the same computer and sitting together physically in front of it.
But I like what you said a lot. A split screen view with separate working areas that we both see, like in a video game, that would probably be nice. Both for local and remote collaboration.
If you are on a shared account, it is even easier by running `(start-server)` and then connecting to it with emacsclient. The only downside is that marked regions are shared between clients.