I miss the storylines / back stories...

Am also a family player. I like the vague storylines that hint at possibilities as in each save I can give a slightly different spin on the relationships and storylines. The replayability and creativity aspect would be seriously damaged for me if the storylines were expanded eg. Take the Calientes in some games Don is involved with any 1 of them and in others I have different twists for them. Too many details or memories would make some of my storylines and family relationships impossible. I love how the game hints at things eg. Johnny Zest being a Landgraab but its up to you to decide if he is Nancy's son or brother or another realtionship entirely.

However i do miss story progression for sims I don't play. I miss having an option for this. They have a variety of on off switches for aging and autonomy so I can't see why we can't have them for story progression too. Before I got mods it was endlessly frustrating having to suspend my own gameplay to progress the otjer sims, giving them marriages and children etc. As you can't create babies in CAS you either have to play those sims or give them instant cjildren and toddlers. As was mentioned above, not everyone can mod for a variety of reasons
The game already has the my households other households split so it would be very easy to ensure that story progression only happens for the sims you wanted (so as not to ruin rotational play).