Thats an interesting model, but I cant think of many projects where the features are added at a constant rate. The deluge of pull requests going to Linux are no

Thats an interesting model, but I cant think of many projects where the features are added at a constant rate. The deluge of pull requests going to Linux are not constant, and probably grows with the number of contributors perhaps relative to population growth of programmers (also not constant). Perhaps another metric is how long after your code is released will you be able to support it? In which case Linux and NASA do quite well.