* They're still working on Clear History, and think it is worth implementing (Zuckerberg is the one who introduces the topic–the interviewer hasn't asked him about it). It's important that users have a tool like this, even if it makes their experience "worse" (i.e. less personalized).

* Clear History is nontrivial to implement, because Facebook was not built with this functionality in mind. And they want a user interface that is more capable than just a single "delete everything" button, because their research has shown that users frequently want to clear only certain aspects of their data (e.g. data shared to a specific service or app via Facebook), so this adds complexity.

* (In the context of a Facebook subscription service, which they were discussing before Zuckerberg mentioned the Clear History tool)–having Clear History is a prereq for any sort of subscription service, but they want Clear History (and all privacy controls) accessible to all users, not as a privilege for certain users.