Sudden though: it we had 3 pin female-only sockets on "everything" we could reasonably go to a split 12V/50V system and it's petty easy to make 3 contact coaxial designs. That way extension cords could take all three wires and devices that only want one voltage can grab it and not connect the other pin. With a little design cunning the plugs/male connectors could have a sliding shield to reduce the chances of anyone getting even 50V. One hidden benefit of this is that people could have ridiculously efficient power supplies that pump this stuff out and only use the portable heaters when they were actually travelling.

This makes me wonder whether we've reached Edison's time yet, and could push 400V DC into the last mile of the grid instead of the 320V peak AC we have now. Or 200V for you people in the US. That would increase efficiency (higher average voltage therefore less current drop as well as reduced inductive losses) and the power electronics to deal with it are cheap. Fantasy, of course, the retrofit costs would make FTTH look trivial by comparison.