UnbelievingScumOnTheOtherSide,
And let me just add that (regardless of the proposed 28th Amendment): taxes based on age, height, race, etc would all fly in the face of the equal protection clause of the 14th Amendment which is why none exist now.
I did not state my rebuttal to your point about Congress raising taxes to 90% on States very clearly. Let me clarify. There is a reason that Congress does not _today_ raise the tax rate to 90% on all American citizens incomes. Under the Constitution, Congress certainly has the power to raise the tax rate to 90% on all Americans incomes. But obviously Congress lacks the political will to do this because of how immensely unpopular such a tax act would be. No representative could survive re-election, and the bill would be promptly repealed and tax refunds issued. Under the proposed 28th Amendment, Congress has even less political willpower because now it is taking on not only the political will of the American people who will never stand for such an absurdly high rate of taxation, but in addition Congress is taking on 50 Governors backed by their State legislatures who have a financially vested interest in railing against any such absurdly high rate of taxation.
But since the 17th Amendment, they have no direct vote on the matter.
The Feds can and have put in a 90+% tax rate before - just not on everybody.
It will be much easier for the Feds to put a 90% tax bite on the states. All they have to do is take over 90% of the function of the states in exchange.
Look how Medicare is going. It's taking a large and growing chunk of every states income. At some point, the Feds just step in and say we're taking Medicare over completely and the states must now fork over another 25% of their revenue. The cycle is: Increase the mandated spending on area X for the state until it's unendurable, take area X over in exchange for another chunk of state revenue
This can happen with education, just with a slow expansion of the NCLB mandates. Any government function can be transferred from state to federal responsibility this way, as long as you don't recognized Constitutional limits on Federal authority.
And given enough money to pay off a few states here and there, there would not be a united front of 50 governors fighting this.