[pjc50]

There are plenty of things which are done, but done badly.

"X, but decentralised" is popular at the moment. Or think of things that people would like to do but don't because it's too much hassle: backup. Encrypt.

Ask people what the hassles are in their life and interactions with technology.

Or alternately, do a cool but purposeless tech demo. I've always wanted time to play with procedural generation.