In Europe, they work because they are properly maintained and cleaned. You have to pay an euro to use the facilities. They should do the same in NYC if they are serious about this proposal.
Problem is, that no one in New York City, other than European tourists, would have a Euro to put in the slot.
I was in Zadar, Croatia, last month, where it cost 40 cents (Croatia recently adopted the Euro) to get into the public restroom at the bus station. A couple of German women were in trouble because they only had a 50 cent coin, but fortunately I was able to give them change.