I would imagine that a touch scroll pad like in the linked video would be a useful thing to have on the left hand side of a keyboard. I could use it to navigate through a document quickly and use the mouse to pick my target.
Games and input devices for games also always design around bimanual input, even if rarely consciously.
Side-track: something almost nobody noticed when the Wii came out is that it's wiimote/nunchuck setup works both for right- and left-handed people. I'm left-handed and I automatically switched to a left-handed input method for my games without even thinking, for the first time in my life! I didn't even realise this until a few months in myself!
And yes, I completely agree with you! Something I forgot to mention is that for certain types of tasks, this kind of input lowers the mental burden for the user (something that Buxton showed in his papers).
If we turn your idea around: laptops come with a trackpad by default. If only OSes would allow for distinguishing between it and and external mouse (for example), then we could already cheaply and easily experiment with this on our laptops!