With the caveat above, a couple of passing thoughts:
(1) I’m still deeply suspicious of where this push to oust Biden came from. The press coverage was driven hard by •something•, and it wasn’t popular sentiment.
AOC’s theory still makes the most sense to me: this came from donors. The obvious replacement is Harris, and I’d be happy with that, but…odds are good we’re instead going to end up with a substantially less progressive candidate than Biden. Alas. (But see 1-3 in the OP.)