I don’t play the piano myself, so I don’t really know a lot about it, but what you could do is examine how techniques in playing the piano have changed over time, for example twentieth century techniques like prepared piano (techniques are good for giving hands-on examples, rather than just a cd or tape), as well as the way in which the piano itself has developed – both in how it’s made, and its position (or lack thereof) in the orchestra.
Hope that this helps...