THAT is the revolutionary power that either will serve representative democracy OR the Republicans will harness to overset it further.
We got a good start on influencing it for good in the midterms, but 2020 will either open the gates to a new era of greatness and widespread prosperity of a progressive liberal republic OR build on and consolidate the power cemented in with the 2010 census of the increasingly authoritarian white male Christian supremacist party.
As for your idea, interesting, but I'm afraid offering a cabinet before being elected president, much less before the primary election, doesn't strike me as even remotely possible. Or desirable. The best qualified and in-demand people simply would not commit to being used by one candidate to try to get elected, becoming identified with policies and processes that may not actually represent their beliefs, and in the process slamming the door on serving whoever was elected (along with a prechosen cabinet). People of top stature don't have to and most wouldn't. This would lead to most or all candidates having to name a bunch of opportunistic, (at best) second-stringers.
As for the future of that first candidate who'd presumably "force" the others to follow suit, I'm guessing it could be very ugly. The other candidates might instead choose to just watch as swiftboaters working for opponents smeared dozens of virtual unknowns to attack the candidates themselves and obscure their agendas. And what about when the cabinet appointees become future declinations 2 years later, as would happen?
The opportunities for partisan ugliness and voter manipulation seem endless to me. Because the majority of people don't bother to properly (thoroughly and honestly to themselves!) vet any presidential candidates, even the one they end up voting for. They're going to do their homework on dozens of faceless people for each?
But, that's just my reaction. Is there any nation that does this, and how has it worked out?