All income 2.5x above living wage (legitimate living wage, not the American government's idea of living wage) and all cash assets (e.g. savings, stocks, capital gains, investments) greater than $2.5 million are taxed a flat 75%, with one flat $10,000 annual refund per child/dependent.
I'm not nearly as generous as Sandman. Also, unfortunately, it's not easy to place limits on the number of dependents. It's not the Duggar kids' fault there are 5,000 of them, and they deserve to eat even if their parents are super fucked-up.
For kicks, we'll call 2.5x the living wage $75,000. Under my plan, Mitt would keep "only" $12.5 million if he brought home $50 million, assuming that he has no dependents, and his tax rate would be approximately 74.89%. Bawwwwwwwwwwwwwwww. For comparison, a single person with no kids making $250,000 would have a ~52% tax rate, meaning they get to keep $118,750. If that person has a house-spouse and 3 kids, they would get to keep $158,000, making for a tax rate of ~41%.