I think it is worth noting that the quotes in your comment are from 12 years ago: http://www.gelato.unsw.edu.au/archives/git/0504/0885.html

I don't mean this to say that you are being inaccurate, just that his current position seems a little different now:

"Again, I'm not arguing that people shouldn't work on extending git to a new (and bigger) hash. I think that's a no-brainer, and we do want to have a path to eventually move towards SHA3-256 or whatever" http://marc.info/?l=git&m=148787457024610&w=2