A couple thoughts:
* The Constitution nowhere proscribes the form or source of elector votes; however, it essentially prescribes that electors represent a choice by citizens of respective States;
* The prohibition that “of whom one at least shall not be an Inhabitant of the same State with themselves” will be problematic to this scheme, as any winners of a so-called popular vote will likely be citizens of the same State should the vote be decided nationally (I know that’s obtuse but the logic is there...);
* By the logic of this scheme, a coalition of 270 EV states could in advance of any election decide to cast all votes for the Republican candidate;
* A practical effect of this scheme would be to launch electoral reform and enforcement voter ID / citizenship and fraud, as these are tolerated until now by the EC isolation of fraud to the states, whereas this scheme would nationalize the fraud;
* The one test-case on this regarding one-man-one-vote in Mass is not a serious test, so I wouldn’t count out rulings on the scheme as unconstitutional;
* Imagine if the Republicans were doing this to the Dems: oh, the outrage!
It does not. Read the document.
You have no idea what you talk about.
Electors represent districts, not States.
Go back and do your homework.