Read Article I, Section 10. This is unconstitutional unless Congress approves it.
See my post#116.
Congress doesn't have the power to dictate to the states how they may exercise their constitutional powers, including divvying up electoral votes. Such a compact among states would be illegal -- in the sense that it cannot be legally binding on any of the states that voluntarily enter into it -- unless Congress approves. But Congress lacks the power to void any individual state's actions under it.
Basically, the proposed "compact" amounts to an informal gentlemen's agreement that provides political cover to state legislatures because any state that goes it alone will be at a political disadvantage relative to others.
No one wants to be the one to go it alone, so they need the assurance that others will be right behind. It's not a binding compact anymore than the Contract with America was a binding contract. It's a political arrangement.