I can't see much downside to this. Not the least of which because doing so he will drag the Overton window of the talking points of the current primary candidates over more towards the center. Normally that happens only after the primary is over and is not easy after right wing social media and Fox and friends and similar have applied some devastating branding to the frontrunners by picking out stuff they say and do in the primary.

Note he spent that much to help in 2018 and he wasn't running then:

During the 2018 midterm cycle, Bloomberg spent over $100 million in a successful effort to help Democrats wrest control of the House away from Republicans.

This jives with my view of him as not being an egomaniac much less a narcissist. His main flaw is being a kind of control freak, he thinks he can make anything better and when he focuses on something,that he knows best how to solve the problem. No humility. Though he is a delegator, he chooses the "delegatees" very very carefully and never stops managing, closely, is famously known to prefer huge open office spaces where he sits with view of what everyone is up to.

I can think of one issue that would easily occur: disagreement with how DNC is handling things. If they disagreed with something he was doing, he'd swat them away like a fly. May already think they are doing everything wrong.

This is why the apology about stop and frisk was at first kind of shocking to me. You'd rarely hear "I was wrong" from that man. But then I thought again: if he thought  an apology  about anything was smart strategy, he would do it.. (And then there's also that he's like a female version of Miss Manners. )