There has been anecdotal statements/blogs from Apple employees about the data privacy. They have said building some internal capabilities or user facing features are extremely difficult or impossible because they aren't able to access user data at the level required.
There is a comment in this thread from an alleged Apple employee that said that, but it doesn't seem like it's possible to send a link for a specific comment. Over the years I've seen comments and blogs posted here in Hacker News reaffirming the same thing.
But to answer your question directly, I don't have any links for those blogs or comments