The Compact is already in operation for the states that have agreed to it. I believe there are 13 of them? The goal is to make the big cities all powerful electorally and to marginalize flyover country.
The Compact, by its own terms, goes into effect when approved by enough States equally a majority of the electoral votes for President (270 or more). It's about a 100 short of that. So it is merely a proposal right now.