I originally thought you meant (and others misinterpreted) elevators in 2-story buildings would not have buttons on the inside, that they would still have a button on the outside. A later comment indicated the opposite, there would be no buttons on the outside either.

I agree with the idea that 2-story elevators could get away with no buttons on the inside. When someone enters the elevator, the door closes, the elevator moves to the opposing floor, and the door opens.

I disagree with no button on the outside for several reasons.

When a user first interacts with the elevator, they need to initiate an action. They have to tell the elevator they need to use it. Disregarding the sheer confusion users would experience the first time they encounter a buttonless elevator, how would a user know their "request" has been registered? Any additional notifications (lights, sounds, etc.) would be extra layers of complexity which are not necessary when a user has a button available.

Pressure plates and sensors are always prone to mistakes. No one stands directly in front of an elevator door. They push a button and stand back for a couple reasons. One, if there is a floor indicator, they can view the current state of the elevator. Two, and more important, people stand back to give room for passengers who may be in the arriving elevator to exit. If I stood directly in front of an elevator, and then step back, how does the elevator know if I am still there, or I've changed my mind? What if I am standing in front of the elevator having a discussion with someone, or talking on my phone?

In a Star Trek future, sensors will know with certainty whether we intend to use a given door which will open at the precise moment needed, but we are certainly not there yet and may never arrive at that fictional version of the future.