How large (or small) is the audiophile market?

Boomers got into audio because we didnʻt have home computers back then.  The hi-end hi-fi market has always been slow and small.  As we boomers pass on, the market will continue to shrink, but there will always be those who love it.

One big problem is that the audio manufacturers are not only competing with each other, theyʻre also competing with the used audio market.  If youʻre thinking of getting into the business, donʻt.

COME ON.  How can you ask, much less answer, this question without setting even broad boundary conditions?

How do you define an "audiophile"?  Someone who "buys $1500 speakers"?  Someone who "subscribes to TAS or Stereophile"? Someone who seeks out the best-sounding hirez content and then listens to it on an iPhone and AirPods?

Is a twentysomething defined as being an audiophile by different criteria than one would use for a person over sixty?

The legal profession understands the simpler the question, the longer the answer.  If the OP is looking for anything like a concise, definitive response, he or she needs to add a few boundary conditions...

I notice that many of the most credible responses here add their own qualifications to the question.

Just sayin’.  Before you can even answer the question one posed by the OP, we need (more conversations?) to resolve the implicit assumptions that underlie it. 

I used to work for a high end art gallery in New York. I was told there the market for people who would purchase $100,000+ artworks was 2,000 people.

So depending upon what level of price point for audio gear, I’d guess somewhere in same order of magnitude.

i know a good amount of upper middle class with basic McIntosh systems probably at $25k total.

But that’s just based off the day point I know.

My opinion is that I think the market is going to slow in a bad economy. It will pick up in a good one. The generation of the 60s, 70s, 80's are dying off. I have a lower cost tube system, Speakers I designed, built, I stream, no investing in clicks and pops. I have a selection of 60 million titles.  Having a high end stereo is dependent on whether you have the desire to invest money in high end audio or something else. Today, we have water sports, 4 wheelers, off roaders, fishing boats that cost 48k for a nice Lund boat, a nice car like a Mustang GT, Challenger SRT, or high perf Audi, Porsche, To Corvette Jag......  My opinion, you need the ears for high end audio, you need a decent room, and a budget you can afford. High performance is not always how much money is dumped. Depends on ears.  You must love music. Rap is not music, sorry. My grand daughter who is in Korean artists loves my system which is lower scale but decent. 

I don't think the market for quality audio equipment will disappear, but I think it will contract. I'm in my late 60s and as a kid the family listened to our stereo (such as it was) for family entertainment. That entailed actually buying physical media and loading it up on the turntable. Recorded music has been commoditized for young people with ITunes and a cell phone-no more "ritual" involved. There are exponentially more entertainment choices and music is more likely to be a background thing while they are working out, etc.Quality sound is not very important in that context. One of my great pleasures is spending a couple of hours, or more, just listening to music and nothing else-my kids (in their 30s) don't get that at all.

I also think the disappearance of brick and mortar stores contributes to the shrinking market. How many young people have actually heard a reasonably competent system? In the old days, audio stores were plentiful and even if you couldn't afford to buy you were exposed to the experience if you were curious enough to walk in to a store. That's not happening much these days.