PeerTube is not really intended as a platform, even less so than most fediverse projects. As it stands, the best way to think about PeerTube is sans discovery mechanisms because I don’t think any are planned. With this in mind, peertube is best thought of as the video extension of the fediverse and the discovery niche is filled through word-of-mouth here and over on the microblogging side.
I don’t think anybody’s tried exactly nebula-style, but there is already https://newellijay.tv which seems to be a kind of video-outgrowth of an existing rural makerspace? Pretty cool project from what I’m seeing