I think the main way that could be achieved is if Kbin and Lemmy had a convenient "upload video" option that actually uploaded the video to peertube. Convenience is king. Back before Reddit offered image and video hosting (and you'd usually upload to a site like imgur instead), there'd constantly be people commenting that they didn't know how to upload their content.
That said, I'm personally cautious of PeerTube. Hosting small images is one thing, but video is something else. I don't really understand how PeerTube will keep running if it gets too much usage. Presumably, like most of these sites, it will depend on donations. I don't know if that will cut it for hosting video. My fear is that it'll be fine with low usage but as soon as it gets too high usage, we might see it going down (and taking a ton of content with it).
NotTheOnlyGamer