I actually really like Japans system they had to inadvertently invent - the north part of the country and south operate on different power standards ( I believe the phase? ). This led to them building MASSIVE insanely high voltage DC to DC connections between the two grids so one side could still supply the other with power. But the other plus is that ( I believe ) one side can also not take the other out or draw too much power. China is investing heavily in super high voltage long distance power transfer and I suspect the US could do the same and use it to connect different areas of the country. Also much lower transmission losses.