Personally, I think that we should ditch the entire tax code, set a flat income tax rate - a single rate that applies to everyone and every kind of income - and a standard deduction of say, 1.5x - 2x of whatever "poverty level" income is.
Such a system is triple-progressive: first, high income earners pay more because x% of a lot of income is a lot bigger than x% of a little income. It's progressive in that poor people pay nothing due to the standard deduction, and middle income earners pay a pittance for the same reason. And it's progressive in that it eliminates all loopholes so there's no way for high earners to game it. But it only works if you eliminate all deductions and special income treatments including the sacred cows (mortgage deduction and capital gains).
Of course this is fantasy; lobbyists for CPAs and for attorneys would never support anyone who voted for this kind of simplification.
And, Congress would f** it up immediately by restarting the "let's use the tax code to reward our donors and punish our enemies" process.
Sigh.