alt Hacker NewsYou are wrong with your own examples.
Github is THE main platform for git. If github doesn't upgrade (and their code has been shit and hard to fix/update before) then the shift will not happen. Because yes, you can upgrade your repo independently, but if there is nowhere to push, no one will do it.
IPv6 is (also because of github) a great example for this. You can easily have an IPv6 address next to your IPv4 address, but a lot of websites (e.g. github) don't have that. Why would a normal company use IPv6 if even the bastion of nerds doesn't use it?
And to Python 2's "eventual migration" I can unhappily tell you, that my company (recently) bought an actively developed tool, that still uses Python 2.
I don't think GitHub is quite as important as that, outside of some specific projects that made bad/lazy decisions (thinking Golang here). If they didn't support 256 I think a lot of enterprises and open source stuff would simply jump ship to GitLab or elsewhere. In the enterprise world it only takes one person to write a security document banning sha1 for this to happen. For that reason, GitHub will support sha256.