Here's my anecdotal take on the topic. I'm 52 and amongst my friends, family and coworkers I can count maybe, off the top of my head, 6 or 7 of them who have dedicated hi-fi setups. And when I say hi-fi, I'm talking about a receiver, speakers, and a turn-table - very mid-fi setups. Of those 7, only one has a dedicated streamer, CD player, pre-amp and amp combo, and a 2-channel system. That would be me. The majority listen to music via streaming services using Bluetooth speakers or earbuds. I think of the 6 people I know with dedicated listening set-ups, there are a few of those set up as home theater/gaming systems where music is secondary.
So while there may be more hi-fi components being sold than ever and at the higher-end as well, that's not because the cohort of hi-fi consumers is necessarily growing exponentially in the under-50 crowd, but because the aging Gen-Xers finally have discretionary cash lying around to invest in systems and the 60+ crowd are replacing or upgrading. Sure, you'll have the 1%ers of the wealthy buying high end setups because they can and want to impress but that is still a small market share of total units sold. We also have a bigger global population as well.
I'm sure over time, the Millenials, Gen-Z crowd will grow into wanting better-sounding systems, but many don't know what they're missing out on and will stick with whole-house Sonos or Google speaker systems that "do just fine" in playing their daily Spotify lists.
A small segment of headphonauts will stick with such setups but upgrade over time and maybe venture into 2-channel setups. But having discretionary funds to spend on those things is a big ask for people who are not dedicated & discriminating music listeners. I have 3 young kids so the idea that I'll be dropping huge wads of cash on components is laughable. I can justify spending $3-5K on speakers but anything beyond that is not a priority for me. I'm happy with a mid-fi hi-fi system.
I know a few younger co-workers who are into listening to vinyl but they enjoy the sound and are happy with a $400 setup and honestly, the technological improvements happening over time make the entry-point into a decent hi-fi system easy to achieve without breaking the bank. I think the future of hi-fi will be the continued growth of mid-priced hi-fi. You'll still have the guys buying the flagship Gryphon and Wilson Audio and those manufacturers will focus on that niche. But companies like Marantz, Cambridge Audio, Bluesound, WIIM will be what a growing number of people will have as their first hi-fi setup.