I find this more reassuring than I was expecting to, because

(3) And finally, there’s actually a reasonably straightforward transition to some other hash that won’t break the world - or even old git repositories.

rather than the entire post being pseudomathematical waffling about why this attack doesn’t “really” matter.

For me, the big lesson here is, within reasonable limits, design your file and wire formats so that they can be extended. Easier said than done, I know.