Code change lines: could be an interesting marker to gain a better understanding of activity of the project. Our analysis so far has been more focused on how people interact with the project as contributors, disregarding information about the volume of their contributions.
Project popularity: implemented stars, forks, contributors, issues,... Looking at PRs specifically might be interesting, too (see #52).
Technical fork: related to #34.
Time to first response: would be interesting to test hypothesis about attracting new contributors. Would need to gather substantially more data though.
Have listed in wiki. Anything we want to have a final look at?