Update: Nov. 14, 2014
Vox has a set of cards on inequality (both wealth and income), and examines the "guaranteed income" proposals of the 1960s (even Nixon wanted to do it). Vox makes the interesting observation on Card 7 about "the fundamental nature of capitalism", that Piketty thinks the relative equality of the mid 20th century needs explaining, not inequality; follow the subordinate link. Yes, the superstar effect has gotten bigger.
Update: April 2, 2015
MIT graduate student Matt Rognlie, 26, has published a paper "Deciphering the fall and rise in the net capital share" (link, published by Brookings), to answer some of Piketty's analysis of wealth inequality. He seems to take the libertarian-Cato position government policy, especially in proping up real estate, is responsible for some of the distortions. I don't think that's the case in my own life. My own family's "wealth" came from conservative, compound-interest-sensitive investment by my father, and a gas well on the mother's side of the family, when prices were higher (the gas well paid for a lot of eldercare). Vox has analysis by Matthew Yglesias here.