> (though of course none of the desktops will understand where it's supposed to be and probably put it in the wrong place, etc...).

Changing display layout on modern Linux desktops is really really simple IMO.

You just open display settings and drag them into the layout you want.

or

xrandr --output $touchpadscreen --below $builtinscreen

Exactly that, proprietary hardware will limit usefulness for anything beyond specially developed Windows functionality.

And, even if the hardware can be hacked for Linux the question becomes, how can it be made functional in a desktop environment independent way?

Been doing R&D for a similar concept for several years, a detached video enabled trackpad. The key functionality which all concepts to date lack, is being OS agnostic and allowing end-user customization of functionality.

It's a good effort, but is likely only the beginning...