If they're good rationalists overall, they could also establish as common knowledge that they both timelessly decide not to predict/estimate their spouse would wish to know something which is known by themselves to be likely to bring about lower total utility to them both than if the spouse had never wished to know it, whether the spouse knows of this or not.
Recently, LWers Will Ryan and Divia Melwani (now Will and Divia Eden) were married, with Eliezer Yudkowsky officiating.
I've been to 40+ weddings in my lifetime, and this was my favorite ceremony yet. Here is the video, and below is the transcript of Eliezer's... what's it called? "Blessing"?