One more thing I was thinking about is that I don't think people are uploading things to YouTube just to have YouTube be declared as outdated in a few decades in preparation for the next form of media. The implicit expectation that most casual producers have is that the videos will remain on YouTube "forever," which really means some vague amount of time that doesn't have to be thought about in the short-term. This is a major difference from television because YouTube can be used for personal expression, major productions broadcast on television are archived by the studios because the finished product is not restrictively large in terms of data, and I don't think people would be happy if the millions of hours spent producing their independent content will be all for nothing in a few decades. To keep all of that content alive in the future, YouTube either needs to continue to exist or the content needs to be mass-migrated to the next form of media.
But what would that form of media be, and what would be the justification for creating an entirely new media platform to succeed YouTube? I find it difficult to imagine what it would look like at this point in time.
People made a big deal about archiving Usenet when everyone started moving away from it. If YouTube has to be archived I don't see how it can be completely accomplished without people who have used youtube-dl in the past gathering up whatever they happened to save before it went down. There's hundreds of millions of hours of video already on YouTube, and unlike Usenet archives only a few large entities have the money and infrastructure to warehouse the entirety of that data.
Saying that YouTube will pass on because media companies always pass on almost sounds as if YouTube is a ticking a time bomb, and after enough time passes we'll inevitably lose a lot of things that brought us value en masse, and the scale of loss will be far greater than in the past because of the breadth of content and the sheer ubiquity of YouTube.