A slightly cleaned up version of my response:
They're parking lots now precisely because of the highway. Delivering people to their jobs in downtown as conveniently as possible from Allen or Mckinney is the highest and best use of the land. Land costs are too high and demand for anything more than parking is too low (though pent-up for something more exists, hence uptown's inflated prices) to do anything.
The parking lot owners are looking for high rise pricing on their land. Nobody can make that work without significant and likely potentially crippling subsidy from the city. And the city is in no position financially to be spending $50 million per project when $50 million is the approximate amount for necessary to leverage this entire project.
So, the thesis behind the idea is to flip the equation. Make public land that is currently dangerous and contributing to the overall dysunctionality of the area, available for cheap. The land sale can then pay for a safe grid of streets, new parks and public spaces for the new development, even new streetcar lines linking downtown w/ Deep Ellum and along Ross Avenue. By doing so, we write down the cost of land which was prohibitively too high while making the area exponentially more desirable. Land costs low, demand high. The market is then unleashed to deliver good urbanism rather than begged and bribed to do mediocre projects. This is the golden goose.
Now for two linkages...
An amazing column by a Harvard professor of history that basically covers every troubling aspect of suburbanism's increasingly bleak future:
Though politically difficult, in the long term public policy should seek to reshape the national landscape to prioritize denser forms of living. Many metropolitan centers, from New York to Atlanta to San Francisco, have fared better in this downturn. This may hold the key to future economic growth. We should take the opportunity afforded by our new consciousness of suburban poverty and push policy makers to encourage the efficient use of sustainable energy, better integration of public and private transportation, and to offer alternatives to home ownership as the signal achievement of the American way of life by taking the dramatic and long overdue step of abolishing the federal mortgage interest deduction. The American dream of suburban domestic bliss has been fostered by sixty years of public policy; a new American dream of sustainable community and solidarity in urban life is also within reach, if public policy once again lends a hand
And lastly, Leinberger has new data on the Millennials and their preference towards Walkable Urbanism (ignore this demand at the risk of the future of your city):
A 2008 SURVEY found that 77 percent of millennials – the generation of 20-somethings – want to live where they are "close to each other, to services, to places to meet and to work, and they would rather walk than drive."