They could, yes. Afaik no extra work was needed on lemmy's side once Mbin changed to report moderators in the same manner (aside from some kind of activity which triggered a refresh of the data)

However, looking at peertube, it looks like they already are using the attributedTo field for the group with a person, which is different from the FEP. For the channel you link in the OP specifically:

"attributedTo": [
  {
    "type": "Person",
    "id": "https://tilvids.com/accounts/thelinuxexperiment"
  }
]

It's possible PeerTube could change to make a /moderators endpoint and respond with that as the FEP suggests, or Lemmy and other software to change to accept this array of actor types instead. I'm not sure who decides these things or if there is an evangelist for FEPs, It's possible this was already discussed on the peertube github as well, I didn't look through all the past issues as there are quite a lot

as far as i know, most (if not all) moderation actions are not federated.

that community is local to Lemmmy, despite the content coming from somewhere else. that lemmy community would be moderated by a lemmy account.

and thats kind of the point. instances get to self-content-control. that said, remote management of your post is a thing.. so you can delete it, edit it, etc.

content creators.. 'posters', would not automatically be moderators of a community because they posted some content into it.