Curious to see all the new interaction paradigms people come up with now that we have something physical that can sense degrees of freedom.

A dumb one off the top of my head:

When reading a book with both screens open, have the outer display show the cover of the book, and closing and opening the screens together causes a page turn. (Unfortunately also a great way to rapidly wear out the hinge mechanism.)

There are some amusing apps which read the MacBook's lid angle sensor. I remember one of them played a creaking noise through the speakers when you open or close it... Somehow I doubt App Store review will let that in for the Duo, but we can always hope.