Thank you for the question. It's a good one, because that's exactly where some of the problems with dual income tax arise.
First, on the self-employment problem, the issue there is to try to separate what's a return to capital and what's a return to the labour of the self-employed. Right from the early days of this kind of dual income tax in the Nordic countries, that's always been a contentious issue. I know that in Norway they have developed a pretty innovative way of trying to deal with this. The broader point I'd like to make is that we wouldn't have to start from a blank piece of paper; we could learn a lot from how things have gone in the Nordic countries.
The second point about potentially high-income individuals—basketball players, hockey players, highly compensated executives, who might have some ability through paying their accountant to do some tricks of transmitting some of their labour income into capital income—is a valid concern. The question, though, is whether you can design a system that can limit that kind of substitutability.
That is the exact right question to ask. I think a good study of the dual income tax would take a look at the experience of the Nordic countries and how they've tried to quell those problems.