>How else do you think the "up next" and "recommended videos for you" feature works? Did you think they were serving up relevant videos purely out of chance?

It is absolutely possible to serve recommendations in a content agnostic way based on other user behavior. That is how the Youtube's recommendations worked at least initially. It should be obvious that they didn't have this ability to analyze content when Youtube started almost 20 years ago.

And even in a content aware system, there is a difference between matching up keywords and understanding what those words mean. That is why an automatic transcript feels more neutral. That just transcribes what is being said. There is no implication of any analysis on the meaning of what is being said.

>If anything a dumb rule like "highlight the subscribe button if the transcript mentions it" is much more benign then a recommendation engine that can somehow always serve you a relevant video.

I'm not saying this feature is scarier than the recommendation engine. I'm saying Google revealing how much they know about the content of the video makes everything they do, including their recommendation engine, a little scarier.