That's exactly what it doesn't do. It versions the checksum referring to a largefile along with the rest of your repository, meaning it's little more than sugar

That's exactly what it doesn't do. It versions the checksum referring to a largefile along with the rest of your repository, meaning it's little more than sugar for a fancy "network symlink". However this should be enough in most circumstances, e.g. to allow representing the complete state of a Debian package repository, without causing Mercurial to slow to a crawl. (Note I just made this use case up, it's just an example)