Well it also depends on what X-cart versions. Older versions did create customer accounts for anonymous users. So it was easier to convert them to real users. So we could create something easily for earlier versions but something for the latest versions would require a good bit more edits unfortunately. I do think it's something that would be convenient.
Feel free to drop us an email if you'd like to see this (
http://www.bcsengineering.com/contact_us/#contact_form ) and mention this thread. If it's not too hard we'll make it a free module, otherwise it sounds like a good small module.
Carrie