linux - Is there yet a solution that affords collaboration with two users, two cursors, one monitor?

I am looking for a solution that is similar in some ways to multiseat, but with one important difference:

I want two (or perhaps n) users to be able to sit at the same monitor, sharing the same desktop environment, but be able to use their own keyboard and mouse, with their own cursor.

The basic use case is that I want my wife and I to be able to collaborate, mostly working on our own things, but occasionally directly collaborating. I want to be able to say, "hey, do you think this is right?" ...and for her to be able to jump over with her cursor, making corrections or copying-and-pasting.

Ideally, I want this to be a linux environment.

It seems that X11 provides for this possibility with a configuration called "Multi-pointer X," or "MPX." Here's the article about it on the X-wiki.

However, I'm surprised to find that, apparently, this solution hasn't been implemented by any window managers, at least in a documented way. Instead, they seem regard "the user" as owning all HIDs, and all working on a single cursor and focal point.

Here's a SuperUser question that contains an answer, but it is unsatisfying as it does not allow keyboard input to different window at the same time.

Since the architecture of GNU / Linux / X11 doesn't seem to preclude this configuration, so I'm surprised to see that it hasn't come of age, as it strikes me as of great use in a number of cases, personal and professional.

Or am I wrong and there's something right in front of me? :-)