I wouldn't call it a "con," but I doubt they're entirely serious. If you want an 18th century constitution, you need an 18th century population that puts 18th century demands and restrictions on government. If you can't get that, if people want more from government and don't want to live with government on an 18th century scale, you won't get what you want, and are better off sticking with what we have -- making it better to be sure, but not scrapping it thinking that you'll get anything like the Constitution of 1787 to replace it. Because you won't.
Who is suggesting that (other than Phyllis)?