Great idea, but they should probably fix the "Check to show domain registration options" first. The user experience should follow the same as purchasing hosting, not force a user to use their domain. There are high possibilities that the user may not have a domain yet the cart does help with offering the option. I had to create a domain registration and site builder bundle and then write javascript that gives the option to register a domain if they don't have one which forwards to the bundle. here's a screenshot.