I use yt-dlp to pull down YouTube videos, and have ad blockers on my web browser (I didn't actually realize that YouTube even had ads until what was apparently years until after they'd rolled out, was stunned when I used someone else's computer).

However, I would assume that if a significant chunk of people go that way and YouTube decides that they're losing out on sufficient ad revenue and/or profiling data doing this, that they're going to start blocking those. I would guess that they can make life unworkably difficult for any third-party clients connecting to their service if they put their minds to it.

YouTube probably doesn't care about SponsorBlock, because they aren't getting a piece of that money. Heck, they probably benefit if it encourages advertisers to go through YouTube rather than content creators on YouTube. But the profiling and the YouTube-displayed ads are probably something that they are going to care about, if push comes to shove and the impact on their bottom line is large enough.

And one more point -- I can believe that the Threadiverse could potentially displace Reddit. Usenet was distributed and was once the norm for Internet forums, and something like that could be the situation again.

But the bandwidth costs of videos are a lot higher than the bandwidth costs of forum text. I am not convinced that PeerTube or something like that will necessarily work at the scale of replacing YouTube. At the least, it's going to be a rather larger chunk of money that has to come from somewhere than is the situation with forums. Someone is going to have to be writing checks, at the end of the day. Maybe it doesn't have to be via watching ads or users getting profiled, but the money's gotta be coming out of someone's pocket.

YouTube also has some of its content creators putting material up to be paid. Reddit doesn't -- well, didn't, as it looks like now they're exploring that -- have that commercial model, where they try to pay people who create content. For YouTube content where the creator is doing it with the aim of generating income, any hypothetical YouTube replacement would need to generate money to cover not just bandwidth costs, but also paying content creators.