Rather than limited time scenarios, they should have a few that are IN-GAME limited time scenarios - what I mean is, the player can access the scenario whenever, but it has to be completed by a certain amount of in-game time.
I love the idea of having certain scenarios trigger when certain in-game conditions are met.
Certain scenarios that involve two sims with opposite traits (like one lazy and one active, or one neat and one slob) would be interesting. I could only think of one specifically that involves the "hates children" trait but I realized after a second that particular idea would definitely come across as problematic to some people.