[gwbas1c]

If you read to the end... This kind of system only makes sense where there aren't major appliances. (Think RVs, off-grid cottages, and developing countries.)

I wonder what would happen if we redesigned the grid today? Would it be AC or DC? If AC, would it be a higher frequency? (Smaller transformers) Is modern DC-DC voltage conversation easier than AC-DC? What voltages would we use?

[bluGill]

It would be both AC and DC. Different applications do best for different things. DC for long distance, AC for medium distances, and DC very short distances - exactly what we do today. Probably we would use a higher frequency, but that is the only change worth considering. Transformers are efficient and easy, and the things that need high power tend to want AC anyway (though they are moving to VFD which can use DC).

The biggest factor is AC is a lot safer. Switches and branch protection devices (fuses) work best on AC. For low voltage DC we can make them work, but for high voltages we don't - instead we put in the protection on an AC side, then convert that to DC.