If you think an ad-pocalypse is bad, then why would they jump to a platform with no ads at all? They'd likely be paying to be on that platform. Also the fact streaming video from a self hosting platform is much more demanding then text fedi instances like Lemmy or Mastodon. Also no way the fedi could keep up with even a fraction of YouTube's creator tools, or their audience which is their bottom line.
YouTube will probably never be replaced. We can at least go for private front ends like Invidious.