Very interesting. I've implemented something similar[1] using a pure Collaborative Filtering approach[2][3], that I think works better for me, but it's unable to recommend unpopular repositories.
The New York Times recommender system uses a hybrid approach (Content Based + Collaborative Filtering) called Collaborative Topic Modeling on top of LDA[4]. It would be interesting to try that.
Really nice links... Thanks! Will take a look at it and compare and contrast for better tuning. :) Feel free to do the same and raise some pull requests :)