No one has mentioned that under such a system, it will matter more than ever who counts the votes, as Stalin famously said.
Precinct level cheating in 100% turnout deep-city Dem pits will be the norm. Ballot boxes will be found for weeks. The fight to harvest the last vote will go on forever. Recounts will last years.
Well, since "voting for President" is not provided for under the Constitution, there is no Federal entity with the authority to oversee any processes which would be necessary.
You bring up a good point. Who will count the votes? Rachel Maddow? Wolf Blitzer?
Even more important: Who will certify the result? In the event of a dispute, who will investigate, and audit, the supposed "national popular vote"?