> And it would all be private. I don't mind paying for my content but I do mind being the product.
Some portions of a personalized, cross-service recommendation engine are a lot more viable if centralized (e.g. any scraping/indexing, and plausibly the personalization itself). Supposing such a service had no intention of you ever personally being the product, what would they have to do in order for you to still be comfortable handing that data over to them?