Nope, frankly given how long reddit's been around and how it continues to gain in popularity I expect it will outlive everything on that list except for youtube. It's the webs default forum and there will always be a demand for a forum on the web.
Reddit's irrelevance is only a matter of time. They're jacking up the advertising and banning anything that offends the advertisers.
Consider also how imageboards managed to remain relevant to this day.
If you're just looking at the 'popular front page', sure, but there's a reason people now search Reddit from Google: there's value in a 'centralized hub' for communities versus Twitter's loosely coupled social graphs.
Reddit replaced all vBulletin-backed forums. You could argue Discord might usurp Reddit but Discord isn't searchable from the web and is logged in a terribly inconducive format.
I follow MMA, and the MMA reddit is the biggest forum for MMA on the English-speaking internet, especially for live events, there's no substitute, and I'm sure its like that with a lot of niches.
YouTube has better and more content than ever. Twitter also has the best and most relevant content, provided you curate your feed. All the stuff happening on academic Twitter, for instance, is hard to find elsewhere.
Reddit also seems to be going down the path of irrelevancy. The content is increasingly mediocre and hivemind-ish.