Or you could write portable software that doesn't rely on reading global input. OBS you give as an example, and it is a good one. They could simply register a D-Bus handler and provide a second binary that sends messages to the running instance. The software is more general in this way as it allows full programmatic control. A Sway user, for instance, could add

  bindsym $mod+r exec obs-control toggle-recording

to their configuration. What's more, they can do this in response to other system events. A user might wish to change the recording configuration of OBS in response to an application opening, and it now becomes possible to write a script which opens the application and applies the change.

If your disdain for desktop isolation is so great, you needn't even use D-Bus. Registering a simple UNIX socket that accepts commands would work equally well in this case.

What's really desired here is a standard way for programs to expose user-facing commands to the system, which is clearly not within the scope of the specification for a display server. The problem with X11 is that it has for a long time exposed too much unrelated functionality like this to the user, and so many apps have become reliant on this and developers have neglected the creation of portable ways to achieve these objectives. A new specification for display servers that excludes this harmful behaviour is a clear long-term positive.