Recently i get this opportunity and i have some ideas too but none of them are really meaningful and have real impact on the world to make it a better place. BTW i'm developer and the PhD thesis should be related too.
If you want to finish your thesis, the best advice I can give you is to <i>select a topic that your advisor is already working on</i>.
If your advisor has already an area of interest, she probably, already has the dataset that you are going to work on. If not you would create that dataset for a future student, in either case your thesis will be part of a much larger picture. Also the importance of the frindship between you and your advisor cannot be overstated.<p>So in reality, choosing the right advisor is 10 times more important than choosing the right topic.<p>(I've adivised over 10 thesis, and reviewed several more)