@kenjit - You clearly spend time on this forum, so should be able to recognize that it's effectively impossible for any discussion to come to a consensus. Also, very few of the most dedicated audiophiles keep the same system for long periods of time, they are always looking to upgrade with the goal of improving things and also to satisfy their unquenchable drive to try new things. Most recognize that the final sound quality results from the "sum of the whole" rather than any individual component.
Even if it were possible for someone to custom design a speaker for a customer which would rely on the designer to understand the personal preferences of the individual customers, the market would be limited to people that had the funds, interest, and knowledge to desire it while also not wanting to approach it from a DIY perspective.
I would also argue that a custom car would be much easier than a custom speaker. For a speaker the preferences are not easily defined or understood. For a car a customer can describe if they want comfort (Rolls-Royce is essentially fully custom) or performance (Bugatti is essentially fully custom). If performance is what you want, you can adjust a car to suit driving preferences based on track using speed as the unit of measure, this is commonly done in racing.
With a speaker, you could theoretically design for a specific person using a specific room, album, and song, but all bets are off if a component were to change, the room changed, or there was a desire to listen to different music. It's a compromise at every level.