[yencabulator]

> For client systems, couldn't there just be a virtual /dev/input/XYZ that Barrier forwards events through

You seem to be asking for kernel thing, not something Wayland. But let's assume you wanted a protocol on top of Wayland to do this:

Why can't arbitrary Wayland clients always see the mouse pointer, snoop on the keyboard, and inject keypresses? Because of security, by design.

Why is it taking a bunch of work to provide that capability in an access-controlled way? Because it's a bunch of work. For example, quoting libei: "However, the events are distinguishable inside the compositor to allow for fine-grained access control on which events may be emulated and when emulation is permitted."

[westurner]

Sounds justified. How is the implementation?