I believe what they're trying to get at here is "tell us about something you care about beyond yourself". Evidence of passion, if you will.

I doubt you'll lose points if they come up with a different expected value for your project than you do, or if the project already exists, or so on.

I prefixed my ideas with "these are some ideas I want to work on". I listed certifiable programming languages, friendly AI, and improved teaching techniques as my three ideas, and gave a paragraph or two of explanation per idea for why these would make the world a better place.