The current system is nice and flexible and simple enough to be safe. Extension cords work well when you are plugging in a bunch of usb devices and tv/laptop/console. But you can also use the same outlet for a hair dryer or a mixer. Higher current devices like ovens, showers, and cars need to be treated seperately to prevent unsuitable parts adding a fire risk. Lack of compatability to domestic appliances is a feature.
Well, it kills 1000+ people per year in electrical fires in the USA alone. We would never allow electricity in homes like this if it were invented today.
> Such a system would need a box in the basement and lots of seperate wires to outlets.
Yes. But if high voltages can safely be used, and the system is safe in case a cable gets chafed, then the wires become super thin like headphone wires, and overall, the whole system could be produced cheaper than existing systems which use a lot of copper and plastic.
Fire is eliminated too, because a high tech solution measures power losses at every connection, and as soon as enough is unaccounted for to possibly be heating something up to the point of a fire, it switches off.
The main disadvantage is that every appliance or device needs circuitry to measure power flows. This is mitigated by the fact that voltage is variable - low power devices could simply run off 5 to 20 volts at sub-1-amp and not bother with any fancy measurement. Only high power stuff would need the high voltages and all the safety circuitry.
I suspect the risk of fire very thin wires and AC voltage is fairly low - the wires will burn out before there is much of a fire risk.
And it could be negotiated up to 100,000 volts for charging cars with a thin cool cable. 100,000 volts is perfectly safe as long as system capacitance is kept tiny, and leakage current constantly measured. In fact, the voltage of the sparks when you take off a fleece jumper are more than that.