Right now, I have structured much of my money in accordance with current tax law. I don't pay any where near the suggested 15% . So, to implement a new flat tax of say 15% on me would be punitive.
So, why not pass a law, after all due study to determine if it's truly a good idea, implement the FT in 25 years. Conversely, or, at the same time, implement the FT on people who hit 30 years of age having grandfathered all people who have sought to take advantage of the current tax structure.
Any variation of the numbers or concept itself are welcomed. I have no idea if it could or would work. It all depends on whether the FT is a good idea or not. It would NOT be for me under current laws. If I was not structured under current laws, I would be in favor of it as I would be paying a great deal more than I am now.