Global inequality is just another excuse people like Piketty tout so they can toss around their touchy-feely "redistribution" policies. It didn't work in communist Russia, or in Italy, or Greece; their the same old ideas by the same old idiots wearing nicer suits. They think since their good enough and smart enough that they won't make the same mistakes of the foolish policy-makers that came before them, which is exactly the mistake all those other people made.
First of all, I'm really confused as to why income inequality is even an issue. I understand the politicians' need to play it up for votes, but I have yet to hear an intelligent argument backed by data and/or economic theory which explains why income inequality is a bad sign even when everybody's real income is increasing. But maybe I'm just closed-minded.
Second, the article doesn't even mention how a "progressive global tax on wealth", of the sort Piketty would pursue in an ideal world, will incentivize unskilled labor and kill most innovation not backed by governments, which are notorious for innovating in the most inefficient way conceivable (only to be expected when the "innovators" aren't responsible for funding their own work).
There are also a number of issues that I could raise about the graph he posted (comparing world economic growth and the rate of return on capital) but most of my questions would be answered if I had a better understanding of where he got his data.
Bottom line, if I read his book, it will only be so I can have a good laugh and then complain about how the world's going to hell in a hand-basket.