This is as much an HCI concept as it is about the GUI.
I think a multitouch pad would be great.
5 fingers, i.e. one hand, would be plenty though, and having one hand remaining on the keyboard allows for faster resumption of typing long text.
My HTPC keyboard already has a simple multi-touch action, two finger to scroll, and I’m sure moving up to five fingers would be perfectly achievable by most users. In fact, in the video above there were only s few times when you’d have to use more than two or three fingers.
I think this is all fantastically interesting, and discussing the subject with people who won’t just shoot down the unknown/unfamiliar will lead to some great things.
I wish I could be more involved with this area of research and development.