I've been thinking a lot about the merits of the (highest income / median income) ratio in creating a society that is a little more resistant to eventual inequality. Rather than setting absolute tax brackets, what if we define tax brackets by this ratio? That way, it will be in the interest of the highest income earners to raise the median income.
That sounds interesting but would probably be a paradise for tax lawyers. You just create a network of companies, one for each income band. That way, an employee never makes more than the average. Of course only large corperations can afford that so that smaller companies will have a harder time hiring talent.
You could probably define company, for the purposes of such a law, that excluded those kinds of structural shenanigans. Basically, define it in terms of its qualities rather than in terms of legal instruments.
I'd also guess that the IRS has already authored those definitions, or it at least a good distance of the way there.