One correlate of ability is easy to measure and impossible to game: your height.Impossible? I don't know about you, but one of the things I find most exciting about this idea is to find out how people really would respond to this tax. One of friends is currently undergoing therapy because she "hunched" as a child, and therefore should actually be a little taller if her spinal muscles learn to relax. Another friend of mine is dealing with a genetic spinal issue that is causing him to gradually lose height. I doubt either of them would change their final choice to deal with these issues, but would it make it easier to delay treatments?
Extreme examples, yes, but these are just things I can observe now, in the absence of a height tax. How would the world change in its presence? Markets in everything, folks.