Everywhere? The point of an explicit pre-nuptial is to opt out of what would happen by default. It's opt-out, not opt-in. If you don't have a pre-nup, then you get the standard pre-nup terms which have usually been established over a long period of time, with detailed rules about homes, children, property etc.

Do you think that’s what GGP meant (or others would most naturally read) in the phrase “I’d be in favor of mandatory pre-nups”? I do not.

Well, that's why I asked my question, ("What are you proposing that's different from that?") because I don't know what he means by mandatory pre-nups, because we already have a mandatory pre-nuptial agreement, and indeed it sometimes kicks in literally before any nuptials.

Clearly they intend something else than a mandatory agreement you sign up for before marraige, because that exists, but they're not really providing any details on how it would differ?