I'm seeing a lot of touch-screen potential for the "is within" series of nodes. It would be great to be able to sample/select moving objects in scenes. This could be done by way of alpha or the depth map. ie. the node would know which object in the scene occupies the space sampled. Another good way to expand the current nodes would be to add an extra "has alpha" parameter that lets the zero alpha parts of a layer be invisible to the sampler and send it looking to layers beneath. That way you can create any elaborate shapes you like for buttons etc.
This composition prototypes a phone messaging app. You can move the avatar or click on it to see a message icon. Clicking on the message icon will reveal a chathead. You can view the message by using the keyboard control, "left arrow."