I think that a revamp of the in-game elevator system would be amazing. Some features that would be good include: custom text to speech announcements when arriving on floors, ability to customise the "bong" sound effect, speed settings, different types of screen etc.

Also, a pretty complex one could be destination elevators where two or more elevators share the same call button and you choose where you want to go before getting in.

Thanks for taking the time to read this!