The first reason the author lists for why this will be bad is only an "issue" on Git hosts that don't allow repo creation on push (which is brain dead of GitHub). Any other host, you push your new repo, and it will see the hashing algorithm, and receive the contents accordingly.

Submodules is a legitimate argument against this, though I don't know how widely this feature is actually used, and similar to the arguments in favor of switching the default branch from master to main, this is simply a setting which can be changed.

I do like the idea of commits having both hashes, and am surprised that idea has not been explored further.

Generally though, I think the author's strongest argument is simply that the change isn't strictly "needed", and all the other issues presented aren't the strongest arguments against change.