The deference cascade has already begun, but the electorate still hopes that they will voice their own "preference cascade." They will be disappointed.
I think it unlikely that both parties will cave to their insurgents: There is simply too much at stake for the established parties to cave. Their delegates can and will pull out all stops to install their choices to oppose any preference cascade. The established media will continue colluding with one or the other delegated candidates; insurgency media will back Trump, Cruz, or Sanders according to their preference.
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Added: Expect a couple of these moments at this year's conventions: