When I first started playing this game, you could only save in the morning. It was odd, but I got use to it and would only replay a day if things really went south on me. When asked, Aphrodite shared her views on this very thread on how she didn't want this game to become a "save before every encounter/event" fest. But later, she added the restroom saves due to demand and I had thought the issue settled. Now I don't use the restrooms, too use to morning saves to break the habit. And like to think I'm pretty good at judging how well my day went. Last time I got the urge to replay a day was due to while having a good sale demo, but picked the wrong movie and lost a few pts with step-sis.
So my suggest is to kick it to those modders that understand code and create that save mod. Base game I don't think it really needs due to varies reasons. Bad/wrong/accidental decisions are a part of the game, and since there isn't a time limit one could easily come back for another try later. For "ending a session", I can understand that one when having to log off due to something in RL. But I've never had that prefect day of play where that wasn't anything more then a minor inconvenient. Could replay any day and likely have the same outcomes.