Submit three short proposals for term project ideas. These will be very general - the design phase is yet to come. Each proposal just needs a paragraph, 5-6 sentences max. Briefly explain how your idea would be an improvement over some existing interface, or meet an unsatisfied need.
For example:
"I plan to create a new GUI for a music player / music library application. Most of the music player GUIs I have used are either so simple that the functionality is really limited, or so overwhelming that it makes it hard to navigate your library quickly and intuitively. My GUI will allow people to tag songs with customized tags and easily browse by tag."
Do not discard an idea just because you think it's too ambitious. It may be possible for you to implement just a portion of the interface (we can discuss this). And remember, your project will be about designing and implementing an interface, not the entire complex software system underneath. E.g. with the music library GUI example, you wouldn't need to create an entire iTunes-style program. Just enough to demonstrate how the GUI works.