Hypothetical question, that I probably already know the answer to...
Let's say enough states enact the law to enable it to take effect, but only just enough, say 272 electoral votes. A presidential election takes place using this new system. Then the census takes place, followed by reapportionment, and suddenly the collective number of electoral votes drops to 266 or something. Do we then go back to the current state of things, until more states opt in?
Article III, Clause 9 of the Compact:
so yep, it reverts back without a majority