What about this ... the failure of New Urbanism to catch on is really a matter of the right idea at the wrong time.
Le me explain ... New Urbanist communities tend to be dominated by higher-end housing. Maybe it's because upper middle class breadwinners are increasingly children of contemporary suburbs. They want something different, something with a certain cachet, so a NU development might appeal to them.
Now, let's take a family with lower middle class or middle class roots. The breadwinners may be children of the city; they could have grown up in a lower middle class 1920s era neighborhood, a place that has its charms but which is more often than not gritty around the edges. All their lives, they've had images of the contemporary American dream as the ideal living situation; a house on a cul-de-sac in the 'burbs, with a two car garage, a big yard, and neighbors that aren't so close that you can see into the rooms of their house just as easily as yours. A NU community might not appeal to them, because it's not like their idea of the American Dream; it's a glorified version of the rough neighborhood where they spent their childhood.
Why another generation? Because we're seeing the emergence of the suburban lower middle class, of 1950s and 1960s era development that is declining like the older urban neighborhoods the generation before. In some cities, the urban neighborhoods of small, old houses are increasingly exclusive, while the older inner ring suburbs are home to the working class. NU recreates the built environment of these now-desirable areas, and thus in those areas are seen as more desirable among a wider range of homebuyers.
In some cities, urban neighborhoods are seen as desirable; these places tend to be booming, affluent regions with relatively little poverty. The urban neighborhoods with the amenities and built environment provided by New Urbanist neighborhoods have been gentrified beyond affordability. Take Denver, for instance ... NU is taking off in that region.
Now, let's go to Buffalo or Cleveland. Unlike Denver or Seattle, there's a larger working class. Many live in relatively dense neighborhoods with a well-connected street grid and pedestrian-oriented retail within easy walking distance; the comfy areas that exhibit the qualities admired by New Urbanism promoters. The folks living there, though, usually want out. When the working and middle class fled the 20,000 residents/mi2 neighborhood of my childhood, they didn't go to the Elmwood, Parkside or North Buffalo neighborhoods, despite the large houses, charming retail districts, and distance from "da' hood." "The houses are so close together." They all went to Tonawanda, or like Mom and Dad, Amherst. They swapped a 1,500 square foot bungalow on a 3,000 square foot lot in the city for a 2,000 square feet ranch on a 12,000 square foot spread. Corner lot, too, so there's only one house nearby ... about 20 feet away from a short windowless wall.
When my folks last visited me when I was living outside of Orlando, I took them down to DPZ's Celebration. They were impressed ... impressed that someone would recreate North Buffalo so well in the central Florida swamps. "It's pretty, and there's lots of people around ... but the yards are so small, and the houses are so close together." Mom and Dad preferred my third acre spread at the end of a cul-de-sac. They were proud that their kid made it out of the city, and was living in the suburban environment that they tried so hard to get to themselves. The house was just like theirs ... a big, sprawling ranch on a big sprawling lot.
In a region where the collective attitude is "suburbs bad," NU will probably be successful; Denver, Seattle, Portland, San Francisco, Sacramento. In places where the suburban built environment is admired and sought after among the masses, like Buffalo, Cleveland, New York and Philadelphia, NU will have a much harder go at it.
What do I see for suburbia in the next 10 or 20 years? Maybe not dominance by New Urbanism, although that would be ideal. I see the increasing dominance of what I call "a kinder, gentler suburbia" -- lifestyle centers that resemble Main Streets, early 20th Century vernacular and Arts and Crafts-inspired residential architecture, suburban streets that continue to exhibit a loop and lollypop pattern, the decreased dominance of the garage door, and increasingly strict sign and architectural design regulations. There will be a few NU-like influences, like roundabouts and front porches. The car still dominates, although the built environment will look a lot prettier from the driver's seat.