Some of the recent developments in Bangalore are heading in this direction. Mixed use is absolutely one of the better approaches to provide a good lifestyle to people. The sad drawback is that you get isolated and will lose the belongingness to the city as a whole. This is not a big deal in the short term, but in the long term, a set of isolated societies isn't that harmonious for the society.

By isolated I don't mean walled, but a natural preference to just be within your conclave.

What might rather work is super fast door to door transit, which in the present is quite unrealistic. Congestion creeps in pretty fast.