Do I understand correctly that GitHub currently doesn't support SHA-256 repos at all, so the author faked a screenshot of what the create repository UI would look like if they choose a really stupid way to add support for SHA-256 repos, and then proclaimed it an unsolveable problem? Selecting the repository format based on the first thing pushed to it is really not a crazy idea.
The submodule problem is real, but the forge problem is entirely just "if forges implement support in a way that makes it painful it will be painful", and that's true of literally every feature that requires forge support.
The submodule problem is real, but the forge problem is entirely just "if forges implement support in a way that makes it painful it will be painful", and that's true of literally every feature that requires forge support.