You might be missing the point. Some examples of realtime collaboration in the world of remote work can be: google docs / sheets, project boards (trello, miro), whiteboarding (jamboard, zoom), design/drawing, or even coding (VS code sharing).

The same technology that makes realtime collaboration (e.g., figma) go is the technology that makes it possible to build high performance single-user apps that you can open on your phone and desktop at the same time (e.g., roam). It's collaboration whether it's two users or two devices from the same user.

The web will go multiplayer because it's the only way to make high performance UIs that are multi-device without locking. The multi-user realtime collaboration bit just comes along for the ride.

Agreed. I chunk slack messaging the same way I do email. I have two channels that I'll take realtime notifications on, but if someone raises those flags without very.good.reason, they'll hear about it. I generally won't see anything on those channels more than once a month.

For special 'war room' projects I'll set up a special channel that I'll pay attention to for real time colab, but those are very unusual situations with a well defined end date.