I agree with you about Reddit being around in 10 years - because I don't see its users having any reason to suddenly depart, given every other large community is largely similar.
I disagree completely. You got the same thing at the same time on 4chan and other places as well.
I think it was less each place having a distinct & unique culture and more the overall culture of the internet was a huge fence between places of business/serious stuff and then the larger messy, funny, sad, sometimes offensive chaos of (mostly geeky or techy type people) side of the fence where Internet culture thrived - it wasn't a place of business, just a place to have fun and not everyone was there.
Because money, that wall has been broken down _from_ the business side of the Internet and business has leeched into almost every corner of our green space - all of that internet culture, funny cat videos, funny meme comics is all very profitable - especially if it's pushed and manicured for the masses using evil social media tactics.
That's the key, I think; the internet and all its culture has become INRT, as a stock that mostly only goes up, feeding on itself in the same way that Disney now only make live-action remakes.