Youtube is the only truly great social media platform left. It pains me to say it, but the bar is quite low! It pays creators better than its rivals and its premium subscription is generally considered good value. Remember - it's both users and creators that need to migrate.
Really, there cannot be an alternative until there's one that can afford to pay content creators the same or more than YouTube can. No content, no platform.
It also needs to be able to distribute the cost for hosting insane amounts of video data, which is notoriously expensive. A single instance could bankrupt a person if it got hit with a large influx of users. Some lemmy instances has to brace for a rough ride as Reddit refugees jumped ship, and YouTube has a lot more users than Reddit. Even a tiny migration could be hell to deal with.
There will also need to be a purge of extremist content from any platform that wants to invite a migration. If all you have is weirdos evangelising dodgy cryptocoins and conspiracy theorists complaining about being booted off YouTube, nobody will want to go.
Peertube just isn't the platform for this to happen. At least not yet.