Does anyone have any idea how the hardware key part worked? I was under the impression my yubikey would only send a key for a specific URL so there would be no way to just forward the key to actual github because it would be for the wrong domain.
For a Linux user, you can already build such a system yourself quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem. From Windows or Mac, this FTP account could be accessed through built-in software.