Again I haven't read the book but I was curious enough to look at some in depth reviews of it and an interview with the author. It's hard to have a deep discussion about it without getting into the politics but I will try and I will apologize ahead of time for the long post.
Though not a millennial, I apparently share the values the author talks about. I was born in 64 and my father was a Marine in the Pacific during WWII. I'm at the very tail end of the baby boom. My home town had less than 1,000 people, we lived in a modest house on a lake. Most structures on the lake at the time were cabins. By the time I finished high school, the vast majority of the cabins were replaced by large year round homes and the "town" was now a small suburb with a population of 8,000. Today there are about 25,000 people living there.
The modest home I grew up in is at the end of a long line of McMansions. There is no way I could afford to buy property anywhere near there though my income adjusted for inflation is a fair bit more than what my parents made.
After living in a different suburb for about 10 years after I graduated from college, I moved to a city because my wife and I spent a lot of our time there anyway. There were quite a few new young families in our neighborhood that came from small towns and suburbs. I suppose we represent the beginnings of a reverse white flight.
I belong to a sailing club that doesn't have room for all the people that want to join. We share a building with a more traditional sailing yacht club that's trying to figure out how to deal with its declining membership. Our sailing club has people of all ages and many of them are new to sailing which is hopeful.
To me there are regional realities that are going to have a huge impact regardless of what millennials want. Membership in our sailing club is fairly inexpensive for two reasons. The first is that the club can tap into a large supply of used boats. The second is that moorings in Minneapolis are relatively cheap. They are cheap because gas powered motor boats aren't allowed on Minneapolis lakes without a special permit. This is a situation that obviously isn't going to exist everywhere.