So, I am in my early 20s, not that young in an absolute sense, but young in this crowd. I disagree with the notion that hifi is dead among young people, though I'll admit it's less popular than in the past.
First of all, there is a lot of interest in headphones among the younger crowd. I have gone to Can Jam in NYC multiple times, the average attendee there is probably about 30. I have seen teenagers as young as 13 or 14 at the event. Most young people start out with cheap headphones or earbuds thanks to prevalence of phones and streaming services, so it's natural that their upgrade path continues in that direction. Since this isn't a headphone forum, I suspect many here aren't exposed to that scene as much, but go visit /r/headphones or a forum like head-fi and you will see what I'm talking about. Given the amount of space (and room treatment) it takes to get good full-range sound from a speaker system, it makes sense that young people gravitate towards headphones, which you can listen to in your own bedroom without disturbing your roommates/parents or colonizing the living room. And with the sound quality you can get from some modern headphones, I definitely see the appeal, although I'll always prefer speakers. It's also the case that modern recordings tend to sound relatively good on headphones -- they make the crispness of synths and samples really pop, and you're not losing as much soundstage because there's less soundstage to begin with.
Another popular "hi-fi" item among young people is powered studio monitors, especially for those who are into DAW music production, which is fairly popular. I have a few musically-inclined friends with nice powered monitors, for near-field listening they sound quite good and I would consider them fully hi-fi.
But I think
@Semanon makes a very good point that high-end gaming PCs have basically taken over the enthusiast electronics niche that hifi occupied for those who grew up in the 70s and 80s. I am involved in the computer scene as well -- I do competitive overclocking involving dry ice cooling and mods. Over the past few years, I have built a bunch of PCs for my friends and for children in my neighborhood. The appeal of this scene to younger people is obvious given how common gaming is and the fact that PC upgrades yield tangible improvements in performance. People are going to be interested in hardware that plays a big role in their daily life, and for most young people that's a PC moreso than a hifi setup. Also, the job market wants people with computer literacy now, and there's less instruction/interest in analog EE generally.
I think the hobby shoots itself in the foot as well. When young people hear "audiophile," they often think of $1,000 cables and other seemingly frivolous luxuries (if they even know what the term means). Obviously no 20-year-old wants to get into a scene where people are talking about their new $5,000 DAC; that's car money. This is another reason headphones are popular among young people: they are relatively affordable. You can get a $400 headphone setup that's considered to be quite good. My goal here isn't to start an argument on the question of tweaking and whatnot. But I do genuinely think the focus on unobtainium gear and expensive tweaks (looking at dealers and mags like Stereophile) pushes young people away. That's one reason I love Amir's work at ASR: it proves that really damn good sound can be had for a couple hundred bucks. It's why I love AK as well; we can post about and celebrate gear regardless of the price point.
PS: I did read the article, Devon Turnbull sounds like a great guy with a genuine love for vintage gear. However, the path into this hobby for most younger people is probably not 2A3 amps or buying VOTs for the dorm room. And I doubt more than 5-10% of those under 30 can afford the gear he sells.