But now the question is: is it still reasonable to design all CPUs for that segment of a segment of customers?
Well, aside from the cult of Mac... They spend the same amount of money as gamers, but for bog-standard commodity hardware in a pretty case.
Gamers are willing to pay three times the price for hardware just to get a few percent more performance. I would claim that drives innovation.
I imagine professional workstations for industries such as software development, visual arts, industrial design, film production, music production etc. are large users of high end CPUs.
None of them uses overclocked CPUs (like Intel's K-series) that's fairly standard for high-end gaming