How so? There would still be 538 electoral votes among the states. They would just be allocated differently.
They vote by Congressional Districts. The electors go to the winner of the Congressional District plus 2 to the winner of the state.
In like 1800, Virginia, Maryland, and North Carolina voted that way. At that time most northern states and South Carolina had no popular vote for President, but electors chosen by the legislature. They were chosen by the legislature in South Carolina until the Civil War.
Look at red states like Alabama (my home state). The blue areas, like our fairly urban areas, would get EC's for Dims. Same with red state Oklahoma (maybe OKC and Tulsa would get Dim EC's and the rest of the state get Republican EC's).
But the purpose of the EC in the Constitution was to keep a few high population centers from controlling the whole country. In the founding of the country, (which was much smaller then than it is now), this meant that the large east cost towns couldn't completely control the smaller population western states (what was "western" 2 and a half centuries ago). Likewise in modern America (expanded geographically westward since the Constitution), the EC system protects less population density middle America (flyover country) from being completely controlled by the coastal elites in the dense population areas.
It's very analogous to why our Congress has the House of Representatives determined by population, while the Senate is determined state by state (each state gets 2 senators regardless of population size). The two houses together gives some weight to what majority wants (House), while keeping the population dense areas from completely controlling the rest of the country (Senate). That's the same mindset that the EC is meant to use for determining the president. That would go away if all states did like Maine and Nebraska and do away with winner-take-all EC votes.