In the name of efficiency I'd say we should cut out the middleman here and set an appropriate tax rate for potential customers of the mega yacht submersible.
Yeah billionaires will never actually effectively spend all of their money. Rather than try to entice them into buying increasingly ridiculous things, we should just make being a multibillionaire financially unviable so that the money is distributed better to begin with.
Perhaps if the tax rate truly rose to somewhere near 99% as individuals reach the billionaire mark, we'd see whether these folks truly are philanthropists or if they just play them on TV.
