Look at technologies that are either at the Peak of Inflated Expectations (on the Gartner hype cycle) or in the process of plunging into the Trough of Disillusionment, and figure out what needs to happen for them to climb the Slope of Enlightenment to the Plateau of Productivity.
Alternatively, build the world's best To Do list app: https://news.ycombinator.com/item?id=11355029