I would be cool to have an expansion that has various different stories, worlds and challenges for sims. I mean we had games like that in the past but they were separate.
The pack can also give us video cameras so that we can film and our sims can watch or have memories they can think back on, new traits, whims (they have been lacking for awhile and need some new ones) and aspirations. Each world can have a different setting and be similar to Realm of Magic in that way (maybe you can't live in them but you can travel and stay there for awhile to do new things). They can bring some new things like imaginary friends back for child sims and once they are teens they can either turn them into a real sim or forget about them (depending on which can affect the sim in different ways such as their creativity skill or mood).
I just wished all sims can enter the hospital in Get to Work any time or something as it could be great for stories as well.
They can also expand on CAS stories.