I would propose that, for now, the contract-less default should be the status quo, because I feel like otherwise you would be upsetting fixed expectations by the back door. But of course existing married couples should be free to alter their marriage terms. After a while I think almost everyone will want a contract that makes the party at fault pay compensation; once that happens, it would make sense to switch the default, but not until then.

Uhm, are you sure you are not succumbing to the false-consensus effect?

Adultery was harshly punished in the past. Even in the recent past, before the 70s, adultery was one of the few admissible reasons to obtain divorce, and lead to unfavourable settlement for the adulterous party. In the 70s, no-fault divorce laws were passed in most Western countries, and adultery was demoted to having little or no role in divorce settlements.
Keep in mind that no-fault divorce laws weren't imposed by dictators trying to destroy the fabric of society or something (*), they were passed with popular support by democratically elected governments, and there is no noticeable political pressure today to revise them, or even to make the type of pre-nup agreements you are referring to enforceable.

Your position largely used to be the default one in the past, and public opinion has been moving consistently away from it for the last decades.
Holding an unpopular political position is legitimate, but what makes you think that public opinion would move back to it?

(* Well, the Soviet divorce law of 1918 arguably was.)