I think you'll get a more accurate view of things reading contemporary sources than his post-hoc justifications of why Mathematica was really NKS all along. If anything, Mathematica also missed the boat on proof assistants, which it should have totally nailed - so if anything, any NKS ideology embodied in Mathematica held it back here as the field verged to being grounded in type theory. (But more likely - ordinary large codebase too difficult to adapt.)

I don't think GitHub will be able to tell you much about how physicists are working one way or another. Physicists in general, and also mathematicians and researching engineers who I suspect make up the bulk of most Mathematica users, don't use GitHub.