Some of those channels have videos complaining quite loudly about youtube, some are tech channels that do talk about the fediverse sometimes, some aren't even aware of the fediverse but might be interested.

It might be worth drafting a message that explains that it won't cost them anything to just sign up to an instance mirror their videos to peertube as a first step. For more technical channels, they can setup their own peertube instance and mirror there - together or alone.

There might be more incentives, but that's for the community to discuss. What do you think?