Based on the trailers and early access there are several things which I think will definitely go wrong unless the developer were very careful when implementing them.
1. Fire Drills becoming vampire BBQs.
Fire drills force all sims to go outside and wait till they are counted/talked to by firemen. That happens in full daylight and when the class is large say bye bye to vampire sims.
2. Rampaging werewolfs beating up teachers. And you get penalized for it.
While werewolfs beating up teachers might not be seen as a bad thing, I fear this will disrupt the class schedule and you not receiving credits for attending class (Celebrities might have a similar effect). And when werewolfs send sims inside a classroom running those that leave the classroom will certainly get detention, not the werewolf.
3. Social Bunny becoming the next take photos of, just supercharged
If you want to instantly build relation and romance you do not even interact with or spend any time with other sims. Just pause the game, open Social Bunny, send 20+ friendly and romantic messages and unpause. Instant relation.
4. Thrifting becoming one of, if not the most profitable profession.
Forget painting, create 30 cheap outfits, sell them for 10k each and with enough followers and a little RNG some of them will sell each day. Who needs real work when you can simply resell the real work of others?
Do you have any things which you think will go horribly wrong after release?