Sarah, this is a great idea and is being done in some places but not too its full commercial potential. I too agree Havanas Urban agriculture is a great model and we really should follow suit. How wonderful that so much of the city is fed by the city?!
What would be fantastic to see, would be councils making this work in council estates in London. There is often vast concreted space in which would be prime for community gardens and hopefully in turn teach the community to eat better as these estates often reflect impoverishment and little to no education on healthy eating.
I hate to be morbid but you only have to look at suicide rates in the world too realise that so many people are completely blind to what farmers go through day to day 'alone.' Australia and the UK (western countries) have extraordinarily high rates of suicide amongst farmers and even their neighbours and community don't know how depressed or the troubles they are going through. If we could send people to these farms to see how hard it is maybe the message would be spread and it would open up a network for farmers to talk directly to us about the hard times? Even better still maybe it would mean they would have someone to talk too?