Interestingly, the website for the National Popular Vote Compact video that purports to explain the "myth" of requiring Congressional approval saves the specific point to the last 30 seconds, spending most of the video on a lack of "federal interest" resulting in giving states free rein.
However, they conclude that if Congressional consent is required, it would not be required until the 270th EV state ratifies it, at which time they expect Congress to relent given that a "majority" of voters (actually the legislatures) would presumably be in support of it, and Congress hates to buck the people (except when it comes to Obamacare, border protection, immigration reform, etc.).
-PJ
Btw, I like your statement “ Congress hates to buck the people (except when it comes to Obamacare, border protection, immigration reform, etc.).”, or rather, anything other than liberal agendas.