At this point we're at "the democrats might have planned for a single surprise, under circumstances that would be both difficult and suspicious to repeat".

It feels... exceedingly charitable to say that is "habituating people to surprise" in any real sense. If anything, I'd argue it has had the opposite effect: if the Democrats pull a second surprise like this time any time in the next couple of decades, quite a lot of people are going to be outraged.

I'm not really sure why they'd want to skip the Primary anyway? If she failed to pass as a candidate there, it would be pretty clear evidence that she wasn't going to beat Trump. If she passed the Primary, she's got more support behind her. It's a lose/lose to do what you suggested