If I’m not mistaken, all of the states that have agreed to the ‘compact’ are controlled by democrats. Were a Republican to win the national popular vote, but not the traditional EC vote, you can take it to the bank that one or more of the states involved would quickly vote to change their law.
Regardless of the fact that the ‘compact’ violates the spirit of the Constitutional method of electing Presidents, consider that some/several democrat states (cough, cough, California) often take weeks to actually count their votes.
One example of where a "compact" *has* been approved by Congress if the Port Authority of New York and New Jersey.The two states jointly control bridges,tunnels and airports located in both states through it.