Obviously excluding videos whose authors explicitly do not want to, or copyrighted content that could create problems for individual instances.

By doing this PeerTube could become a kind of youtube database of quality content, excluding shorts and toxic/futile videos. What do you think of this approach? Could it make PT more attractive, or would it create problems for the platform?

I'm sure many creators would do it themselves but don't have time, or many would do it but don't even know about the existence of the Fediverse. Perhaps you could start by making “fan channels,” with all the most important and significant videos on a youtube channel (so without having to stay up-to-date on recent releases).