One argument this article ignores is the issue of federalism. The enactment of the 17th Amendment was the first step in chipping away at federalism and this new proposal almost completely destroys the notion of federalism. I like to think of the Constitution as a contract between three parties - the people, the states and the federal government. More and more, the states are being shoved out of any meaningful role not only in area of electral matters but in federal mandates requiring state actions and state spending. The concentration of power solely in the federal government is more dangerous than most people realize.
That's an interesting take. It's a shame the GOP lost contact with that issue after about 1983. State Governments are really becoming more and more like the human appendix.
However, it was re-affirmed in Bush v. Gore that the state legislatures have the sole power to determine the means of choosing electors. So I don't see how these compacts are unconstitutional if they were established by the legislatures.
But IMO they will never get a majority of states because of the nature of the Electoral College itself. I doubt Texas would ever go along with such a proposal, and that means small states and one more large state, such as Florida, would block such a move.