Video hosting is way too expensive and complex to be decentralised.

Yes I hope, but I don't see it happening. Creators will go where the masses are and where the money is.

YouTube is a very different scale of platform... There's probably ways that it could be done, and I know things like PeerTube do exist, but... Storing video is expensive, serving video is expensive, transcoding video is expensive... While I'd love to see it, I'd also worry a little bit about the retention of videos over time. YouTube's video archive is kind of insanely valuable, and it'd be a shame to have it disappear. Not that I necessarily think it's safe in Google's hands, mind you, I just worry that people self-hosting video would drop out pretty quickly.

fediverse YouTube alternatives

Yea, so who's hosting the videos and providing the bandwidth?

Well, PeerTube exists, but IDK how good it actually is since basically no one uses it. I also think professional content creators aren't going to like the Fediverse very much since there is significantly less money in it, but for hobbyists it could work. Of all the big social media platforms, video hosting/streaming is the hardest case to replace. It'll be interesting though. I hear PeerTube works like torrents.