I think people need to be cautious about extolling the virtues of how "their parents and grandparents lived when they were growing up". I am 66 years old - I'm one of those grandparents. And honestly, 90% of MN posters will be manning the barricades if they had to live like that!. Oh it sounds lovely and glorious...
We'll do away with the the shopping malls / centres, and actually we should probably also do away with online shopping (all those transport costs etc), and we'll all nip to the local butchers, deli, greengrocers etc. Of course, they'll be so small, so there will be limited stock and prices will rise because, like it or not, there are efficiencies to be made in mass selling both in terms of range and volume. Hmm, and of course where people are poor, there will be little point in opening a shop because they won't buy enough to make it worth your while opening.
Hmm - all that inconvenient school choice stuff over and done with. You will send your kids to the local school and that will be the end of it. If you are unlucky enough to have a failing school then tough, suck it up.
I grew up in a 20 minute neighbourhood. Well actually it was a 30 minute neighbourhood because that's how long it took to walk to school. Believe me, nobody wants to grow up in that poverty and deprivation. Yeah, school, corner shops, doctor, dentist were all within walking distance, but we had nothing like the degree of choice that people now have, and you lived with what you had for better or worse.
Until we tackle ingrained deprivation and social injustice, then the 20 minute neighbourhood, if it ever happened, would simply reinforce and worsen existing deprivation and only benefit the nice middle class neighbourhoods - although in many cases some of those are perilously close to "sink schools". Our local worst performing school is next to some fabulous middle class areas where all the parents fight tooth and nail to get their kids somewhere else, and pupils are shipped from the other side of the city (nearly an hour by bus) to fill the places. There would be rioting on the streets if those nice people were expected to send their children to the local school.
A 20 minute neighbourhood might contain what you need for life but it can also be very limiting - 95% of the kids where I grew up never left there. That wasn't because it was so great, it was because they never had any other options. And their children and grandchildren are also still largely trapped in the same life they had, just with a modern twist.
If we want to make this work, the past is not the model that we want to use....