Pertaining largely to the question of who would buy such a cd player, read "The Millionaire Next Door"; most persons with net worth wealth (not just high income coupled with high expenses and low net worth) would never dream of spending so much on electronics. There are exceptions, but typically the truly wealthy live very conservatively. That would put the majority of our systems, and even many individual components, beyond what they would spend.
In some ways, I'm sure there are audio junkies who can be compared to the person living in an apartment, who has no savings or retirement plan, yet is driving on lease an expensive automobile. The appearance of wealth, without wealth. So, many audiophiles probably have high end systems but are not net worth wealthy. They are the one's more likely to buy the $20,000 player. High income coupled with a high cash burn rate.
I'm sure there is a discernable difference in sound between a 4k and 20k player, but net worth millionaires as a group wouldn't care - they would state that even a 4k player is too expensive for what is obtained from it. It's something they don't need. It's one of the reasons they became wealthy.