It def sounds like a great idea and I wish it would work but just putting fruit trees and vegetable plants in the city won't end the way you think it will.

I worked at a Community Garden for 3 years in the City. Ppl would just pick veggies/fruit, take a bite and then throw it on the ground. And the amount of water needed crazy - esp for fruit trees.

Having gardens in city centers is more about educating ppl and teaching them how to grow it on their own than it is about providing them food.