Ask HN: Themes for a M.Sc. Thesis in Machine Learning/Big Data

Hi, it is wonderful that so many curious and smart people read and share in HN, so I am going to ask for your help.

What would be an interesting & feasible research project for a M.Sc. thesis in Computer Science in Machine Learning or Big Data?

I see two main paths: pursuing a theoretical theme (e.g. a new model or optimization technique) vs. applying existing technique to a new business problem. What other paths are there?

I'd really like to do something related to software engineering / programming languages, since there is so much data on open source projects on GitHub.