I loved the skill challenges in Sims 3. I also liked the fact that completing each one unlocked a special ability of some sort; some of them were better than others, so I made sure to do those on all of my Sims if I could.
It's similar to aspirational gameplay (finishing every aspiration in the game, the way that I try to do), except that many aspiration reward traits kind of stink. Most of them just don't do anything at all, or do so little they're valueless. For instance, I absolutely hate getting the Hero of Strangerville reward trait; you'll start getting trash in the mail that's almost all spoiled cupcakes, which is absolutely not useful, but is vastly irritating to have to delete that trash all the time. And the reward traits from the two location aspirations - City Dweller, and the Komorebi one - are really completely valueless. Some of the reward traits are only useful if you're actually doing the aspiration; afterwards, they don't matter so much. Then again, reward traits like Naturalist from doing the gardening aspiration are VERY useful, so you never know.
So if they do add something like challenges, I hope they make the rewards meaningful, like they were in Sims 3. They haven't done that great of a job with reward traits in Sims 4, though, so I wouldn't have my hopes up too high.
