I don't see any good coming from Biden taking a stand one way or the other at this point, I wouldn't be surprised if he isn't sure right now other than wanting to keep it on the table. Could be a great bargaining chip a few months from now if he wins, or there could be some other reason that pushes him one way or the other.
There is no reason to keep such a dumb idea on the table. Denounce it or own it. And if you're threatening to change the number of justices on the court to use as a bargaining chip, that's literally undemocratic.
RBG denounced this stupid idea by the way.
Schumer can't just make DC and Puerto Rico states. He could allow a vote on the Senate floor, but PR or DC becoming a State would require a bunch of other votes as well. Quite democratic.
This doesn't make the intention undemocratic. It just means his insanity to change the rules will be stopped by democratic procedures.