That's my biggest fear.
(and btw, they do say "twitter")
If my peers are any indication, a whole lot of TikTok, Reels, Twitter, Discord, and other such mind-numbing platforms.
The types of platforms I would consider 'substantive' (or, at least, more substantive than those platforms) are definitely on the way out.
The few times friends have seen me browsing Hacker News or a certain Mongolian basket weaving form, the first thing they comment on is how confusing the interface is, and how old the site looks.
I truly don't understand the mentality, but if your site doesn't take three seconds to buffer a simple text drop down menu, and have JavaScript elements load in mid-scroll that bump elements around the page making you just barely miss that button you were trying to click, then your site is seen as 'inferior' or 'sketchy'.
Perhaps I've just had a bad sample, but I've experienced a variety of different environments by this point, and by and large, I've seen more people in my generation act in that manner than not.
It's true that HN looks old - it looked old before you were born, probably - but (a) I have no idea how to change it, and (b) the whole of HN is a long bet on plain text. If the smartest young people lose interest in reading, I'm ok with HN dying for that reason. I just don't want it to die for any cheaper reason.
I do find that my peers that now read HN used to be judicial about curating a Reddit feed and mostly otherwise limited on other sources. Short-form content is addictive and as nearly as unavoidable as sugar, but many of my brighter peers work on reducing that intake. Long-form YouTube is also something I find to be a marker of someone who is seeking knowledge. Many of my peers do scroll Twitter and TikTok all day, but I find that those who are easiest to chat with are those who have already scrolled HN today and want to discuss a particular article they know I would have seen. I've had conversations that start with "Did you see that TikTok?" and conversations that start with "Did you see that article on HN?" and the latter is always more engaging.
That said, it's a commercial closed-source single point of failure.