I read that this has indeed happened to some degree around Portland. However, Portland has a regional government empowered to force cities to approve such construction. San Diego has no such government, and likely never will. One proposal in the last two years was to create a regional government which could force cities to build roads they don't want--mainly, the area freeways proposed in the 70s that were deleted when several cities (including my hometown of Poway) incorporated with that aim in mind. That legislative proposal was strongly defeated. Why would it be any different if you substituted housing for roads?
It's silly anyhow. Look at housing trends in this county and you'll see it's true. People camp out to buy into new developments of suburban tract homes, and pay thousands of dollars over the asking prices to get them. These are detached single-family homes with (albeit small) lots surrounding them. Some of those who cannot afford such housing, either new or on the retail market (including yours truly) buy into townhouse subdivisions (which have nonnegligible green spaces within them) as a stepping stone to that single-family home.
This is the demand in the marketplace. The demand is not for dense housing of the type supported by "smart growth" proponents. When that demand is not met here in San Diego, many, many home buyers drive up Interstate 15 to southwest Riverside County. They buy in Temecula or even Lake Elsinore, where prices, though rising, are much cheaper. They suffer a hotter, drier climate, and commute times exceeding an hour to reach their San Diego jobs. That's the price they're willing to pay for the type of housing they want.
The median home price in this county passed half a million dollars this January. If Proposition A passes, I can't see any reason why home prices in the county would not rise further, even faster. The law would artificially increase the scarcity in the housing market here. Econ 101 tells us that would drive up prices, increasing the incentive to move out of the county. I-15 between Escondido and Temecula is already heavily traveled and congested during the rush hours. I can easily see that becoming gridlock joining that which already plagues the length between CA-52 and Escondido.
Sure, you might try to widen I-15 some more (they're already adding lanes to it between 52 and Lake Hodges,) and all the way to Temecula, but that's going to be a hard fight. The same Sierra Club fuckwads that back Prop A will oppose it. And there are natural limitations to how wide you can make a road, like when you run up against people's back yards.
So at some point, something's got to give. It would become too expensive to live in San Diego, and too difficult to work here and live outside it. Would it burst the bubble? If it would, when is the right time for me to sell my house and leave town? What are they "sell now" signs I would look for? Where should I go? I could stand to move back to Chicago--after all, I was ready to do it last summer. Such a price spike here should give me enough profit I could afford to buy back there without moving to bumblefuck with the parents ( :-) ) But is there somewhere else worth considering, if it comes to that?