Is the idea of audiophile listening a dying concept as boomers die off?

No. 
not in my experience. 

@kerrybh    +1   Horse racing has a very similar analytical structure(decision making) when compared to High End Audio! 

@rok2id

Greed is the answer.  They seem to have  forgotten that you can't have an affordable flourishing market for Prorsche, Ferrari and Lexus, unless you have a flourishing market for VW, Fiat and Toyota.  Otherwise, it's all on borrowed time.

As The Frogman always says, The Unwashed Rule.

Aren't Toyota, VW and Stellantis(Fiat-Chrysler) #1, 2 &4 as far as sales worldwide? What could be more flourishing?

I went to a private MBL event and the actual owners/buyers there were in my age bracket and slightly older, which is 40s/50s. 

Axpona, on the other hand, was likely more of a demo in their ~60/70s.

In my case, I had to plan months in advance to attend Axpona and blocked out a weekend.  Despite this, I still was only able to attend Friday.  It'd be very difficult to go to regular meetups or events, which I'd imagine is true for many working-age audiophiles.

Those audiophiles who can visit Axpona and similar shows seem both highly dedicated to the hobby and have money and time to burn. That's a hallmark of an older generation.  

Plus, music development, production, and consumption is changing - vinyl resurgence notwithstanding. The ease of streaming trumps fidelity for many. And since most younger don't ever have the chance to listen through a high end system, that remains a barrier.

Plus (again), with Sonos and soundbars now delivering such (relatively) decent sound at affordable pricing, I would venture that many don't see the necessity for fidelity - especially as the video/visual component of domestic entertainment is much more engaging than it ever has been.