> I don't think it's too long before I can switch from one window to another by just looking at it and twitching my eye.

Most X11 window managers support the option for Focus Follows Mouse, where simply hovering over a different window will make it the active window, and after a short delay, bring it to the front of the window stack if necessary. Just combine this with "Multi Pointer X" and a gaze tracking camera that acts as another mouse input, and you could have what you're looking for...