First, a quibble. You write that "new research has shown that IQ is largely shaped by early childhood development." I'm afraid that the latest peer-reviewed research (as opposed to popular books cleverly marketed to neurotic parents) has conclusively demonstrated the opposite - that IQ is largely (approximately 60%) heritable.

A recent colloquy between Frank Sulloway and and Jack Kaplan in the New York Review of Books provides some of the relevant data. But I should add that this research should hardly undermine the egalitarian project. As Frank Sulloway notes:

This general conclusion [i.e., that IQ is largely heritable] does not mean that environmental influences on IQ are unimportant. On the contrary, abundant evidence has shown that family environments make a substantial contribution to intelligence, especially before children reach adulthood and especially in impoverished environments that do not allow for the full development of genetic predispositions.The increasingly evident portrait of human development that has emerged from these twin studies is one of nature via nurture, as people growing up are drawn to environments that provide the best outlets for their inborn dispositions and abilities.

One other thing. In asking "if Richard Herrnstein or Uncle Ron were born in today’s America, could they still make it to Harvard or Scarsdale?", do you honestly mean to imply that in the post-civil rights era, there are more barriers to social mobility than in the 1930s or 40s? Recent generations of immigrants, from the Asian influx of the 60s and 70s to the emigration of Soviet Jewry in the 80s and 90s (and every group in between), who came to this country penniless, might beg to differ. Free public education is an absolute good, but the success or failure of any group depends on more than their economic circumstances.