Okay here's a question: who is Zuckerberg's base in the Democratic party? I can't see him winning IA, NH, or SC, and if he can't win at least one of those, he has no path to the nomination. And you can't just handwave "MUH MILLENNIALS" because there's no proof in polling or otherwise that Zuck has any special appeal to them.
Well-educated progressives, possibly African Americans and northern White rural Democrats as well. New Hampshire is probably the easiest state for Zuckerberg to win, which is why Zuckerberg is trying so hard to build his credibility in Iowa. Zuckerberg's best generation may be millenials, but his base will inevitably be largely Generation Xers with a large smattering of Boomers.