I am not sure I would like the game to control difficulty with levels. I already feel the game is controlling our gameplay with making us do things with quests etc to achieve in certain areas.
If I want to have a bit of a challenge I will take up a challenge someone has designed by withholding certain aspects of the game to make it harder for our Sims to achieve. Also the game already offers challenges you can select on a lots to make our Sims lives a little more difficult if you feel inclined. I personally haven't tried them apart from putting in the helpful ones to give my Sim a helping hand getting skills. The problem is with the Sims 4 is there is too much for our Sims to keep happy unlike in the Sims 2; for example when social went down it went down quickly and suddenly the social bunny would appear and pick our Sims up giving them a little bit back so they could try and raise it again. That is something I miss in the game; the fun animations when things went wrong or when there was a celebration or happy occasion.
I already feel that the Sims is slowly drifting away from it's original conception of a life simulation. I still continue to play as I enjoy the Sims, but it has certainly changed from the game I played in the Sims 1 & 2.