The replacement may be AI generated content or something.

Let me go into wild eyed futurist speculative mode here,

1- AI/LLMs are basically a response to the enshittification of Google. The reason this tech is so good and useful is because for years Google rewarded SEO optimized content a.k.a. long winded articles that repeat the same words over and over again and take ten years to make a point, which after training on all that gunk, your LLM can now do in one paragraph. The Google search monopoly gave rise to this lengthy word salad web content and blanketed the earth with it. The AI summarizer arose as a natural response. The web as we know it may now die.

2- The software industry seems to gravitate toward a layer cake of monopolies. E.g. we have Microsoft monopolize the OS and app platform, it becomes so awful the government even tries to put the brakes on it, partially succeeds, then we get the Web application platform. Sitting in a browser on top of Windows and others. Which Google goes on to monopolize. One may suppose that another platform will be built on top of this, which will be unmonopolized for a few years, and then someone will monopolize and enshittify that too, paving the way for the next cycle. It's turtles all the way down.

3- How this pertains to YouTube, well in the near future I suppose someone could ingest all of YouTube, and create AI versions of it, exactly like what was done with the web. And they might even get away with it once we set a bunch of legal precedents that this is not a thing you can get sued for. Presumably the AI platform would need to be different or better in some way, so perhaps we'll see a video platform where all the content is generated on the fly by AI, and you can get exactly what you want because it was trained on the videos that humans made. E.g. you can simply tell the AI you want to watch a comedy show called Three and a Half Horses where all the characters are reverse centaurs, and it will spin up as many episodes as you want until you get bored. And YouTube will continue to be an aging monopoly for decades, like Windows, but no one will really care because we'll be watching horses deliver Seinfeld quality jokes [1]

[1] It's not horses and it's not as good as Seinfeld, but someone's already doing this. So all that remains for my prognostication to come true is for a financial crisis to happen, at which point the government can use it as an excuse to print a random $500B and give it to a politically connected billionaire intermediary who will invest a fraction of it into the engineering, and history will continue to march forward as it does. https://en.wikipedia.org/wiki/Nothing,_Forever