YouTube does have the advantage of scale, I wouldn't expect a federated solution to match their condition, but I'm hoping it can become good-enought as an alternative.

PeerTube isn't going to provide a solution, they explicitly state this in their FAQ. But there's no reason why other platform couldn't handle monetization AND federate through AgtivityPub (or its successor). If Nebula or Patreon wanted, they could join the federation and make some videos accessible this way. The one holdout would be video that are only accessible to paid subscribers, they wouldn't make them freely accessible via a federation.

From the PeerTube FAQ:

the uploader can display a support button under the video [..]

We did not go any further, as we refuse to tie our code to a particular content funding method, that might not fit all communities and deter others. It's the reason why we encourage developers to use the PeerTube plugin API to create their own monetization system.