Silly idea seeing the lights in the game can be set to come on how ever you want by clicking on them. 2- lights automatically come on the minute your sim walks in the room unless you have them set to not come on. Adding a light switch is possibly going to conflict with the base game programming and probably why if they add them they will just be decor anyway.
Don't get the point, as realism is what you make it. Sims is far from realism - I mean you can set how long a sim lives, babies take just few days to be born, every sim has a ghost form that communicates with the family and friends, sim teleport every where and make hourly wages most of us could only dream about with out ever needing an education. Really - where exactly is the realism anyway. It is definitely NOT in the Sims. LOL.
Now a days though you can already set lights to motion sensors to make the lights come on when you enter a room - just like the sims lights normally do. That too is realism as it happens in real life if that is the same reason you need light switches. In the sims I don't really want wall space to go to light switches to be honest so I hope if it did come in the game - maybe in a build pack, it will remain an item of choice.
Personally I like motion sensor lights idea, and will be glad when they are every where, in real life, if for nothing else but a safety feature in homes.