The latter half of that statement is the expected executive speak about everything being on the table, but the fact that Sandberg specifically mentioned subscriptions so soon after Zuckerberg hinted at a paid version of Facebook is worth taking note. Neither executive has talked about what might differentiate a paid Facebook experience from what the site currently offers -- but if it's more privacy protections, a lot of people will probably at least investigate signing up. It wouldn't take a lot of Facebook's massive user base to turn this into a notable revenue generator.