or, if I really wanted to keep a save private, I'd save it locally on my hard drive , upload the .cps file to some file upload site, and share the link with someone through private message
Instead of a password, I would probably do private saves that you can give access to a list of other usernames to either edit or view. And anyone else that tries to view it will get an unauthorized error.
Something nice to have, but I can't see myself working on website changes any time soon.