I wonder if they wait, and spring someone at the last minute, if that person would look wonderful, and not enough time to get the negatives out.
The convention is the logical time to “make a move” for a nominee.
A replacement can give a stirring speech and get the delegates all revved up on TV/Internet etc.
Between now and then—the question is what do they have Biden say—it would make their life a whole lot easier if he said he was not running for re-election (health reasons) and he was freeing up all his delegates to vote for whoever they want in an open convention.
Then the Kamala issue is side-stepped. She is on our own like everybody else.
But—just to be clear—I do not believe for even one nanosecond that Biden has any agency in this matter. He will and must do exactly as he is told.