[Edit: Why isn't amending the Constitution a hack? Because it's the recognized mechanism for changing the rules.
What makes the compact a hack? I guess it feels like a hack because the expectation is that, if you're going to change the way the president gets elected, you have to change the Constitution - and therefore having to withstand the full level of scrutiny that such a change would involve. Changing it within the parameters allowed - just barely - by the Constitution is not technically a hack, legally. But it's still feels like a hack to make the change without as much scrutiny, and without the need for the massive majority. At least, so it seems to me.]
In any case, my point is just that a constitutional amendment isn’t required and this is totally above-board. The odds of an amendment being ratified are far lower.
From the Wikipedia article, the only question I see is whether the agreement requires Congress to approve it or not. There seems to be no question that the agreement is allowed and would work.