I'm really not sure I understand the rationale here. The Dem field is already very crowded and it's pretty late for a new candidate to start up. Yes, he has good name recognition, experience, and a ton of money, but he also had some controversial policies during his time. Much more interesting would be if he ran as a Republican (as he did when he was NYC Mayor) because that field challenging Trump is incredibly weak right now. Some of the political pundits I listen to also argue he should just buy Fox News and de-radicalize it, not sure if that'd be helpful or just lead to everyone watching a different network but an interesting idea