As long as neither of those people have any existing/active declaration of marriage to someone else, then it would be valid and in force until otherwise revoked

As long as neither of those people have any existing/active declaration of marriage to someone else, then it would be valid and in force until otherwise revoked. There being an ability revoke means you still need government permission. The only difference is that we would assume a default answer of "Yes" when one asks. This seems like a odd point to make. Weddings and marriage go hand in hand. Perhaps I was being a bit pedantic but I also wanted to emphasize that there is a very big civil/secular aspect to marriage.