Quantitative user studies of how people use Tor
Run a quantitative user study of how people use Tor. Many, many people want to know the top 100 destinations seen by tor exit relays. We'll need to figure out safe ways to collect this data in bulk, analyze it, and publish it for others to use/see/manipulate. Further questions involve top destinations over the day, weeks, months, and years for the tor network at a whole.
The current answer may be "there is no safe way to collect this data", but we won't know until we do some research and arrive at an answer. A few researchers have simply recorded all traffic or samples of traffic, from their exit relays and then run afoul of ethics boards and human subjects ethics at their institutions.
Researching a better method, publishing the method, and testing the method in a simulator may be one possible process.