This article says if you manually enable the experimental new code today then “you can't push code to GitHub” and that old and new repos “cannot be mixed”.

The git transition document talks about keeping a bidirectional mapping between old and new hashes, and converting between the two when pushing to legacy repos:

https://git-scm.com/docs/hash-function-transition/2.55.0

I suspect that’s what gitbutler.com means when they say that, although broken today, everything “will almost certainly be fixed” when git 3.0 ships.

While I’m sure they make a good argument in the hash theory section, I’m less inclined to believe the “train wreck” part of their post.

If you upgrade your house and leave the roof off then yes, it will be a “costly mistake” the next time it rains, but if your plans say you intend to put the roof back on then I’m not sure how I am supposed to interpret a blog post warning of the perils of a roofless house.