I don’t believe Apple about them not sharing data with 3rd parties as they explicitly give themselves the right to share PII with 3rd parties for whatever reason. It will probably be marketed under a “improve your Apple user experience” pitch of something of that sort.
I am also skeptical about take-up among services. You would be limiting your options to just iOS/MacOS users and as per Apple you wouldn’t get data (realistically I think it would be smaller resources that wouldn’t get data from Apple). So why offer this?