Yeah it would have to be something external. Ideally something locally hosted using yt-dlp. And incorporating sponsorblock so it doesn't have to weed out bullshit sponsor content out of the summary.

Basically downloading the video, trimming it with sponsorblock, running through whisper to transcribe and then making a readable article with an LLM. It would not have to be hard. I'm surprised it hasn't happened yet, not from youtube itself indeed for reasons you mention but still.