Story progression is one of those things I love in theory, but it's terribly broken in the Sims 3, so I can see why they got rid of it. In an ideal world, there would be the option of a modded one on par with Twallan's available in the Sims 4, but in the meantime, it's the player's story or none, which is not necessarily a bad thing. It's better than creating a family and putting them in town only to have them randomly move out (like they did in early patches of the Sims 3) or having the game kill off babies and toddlers born to unplayed households while keeping elders alive, to replace them with townies that all have the same default face. I admit that I will not play the Sims 3 with an unmodded story progression. I would sooner turn it and aging off and do it myself. I find that tedious, and I'm disappointed I'll have to do that in the Sims 4, but I do prefer that to a bad story progression with no mods.
Has there been any mention of downsides to household switching in Sims 4? In the Sims 3, you lose your active wishes and there's a good chance your sim's career could be changed, or they could break up with their partner or ruin other relationships because of story progression. Inventory is also at risk, as I would not trust leaving something like a collection helper in an inactive sim's inventory. If there is a way to ensure nothing will change with the sims you leave behind while you take care of other households (even if it's just to play them to have them have a baby or get married) then I find the notion of having to do rotational play far less frustrating.
Also, has it been stated that the new townies the game generates won't all have the same default features, and will we be able to put them in CAS to change their inevitably mismatched, random, and inappropriate outfits (yes, I'm thinking of you, paparazzi in speedos and the Ambitions hospital gown!) without switching to them?