I think airlines could pre-wire all seats to be able to provide 110v supply if purchased with your ticket or on-board as an add-on. Then have an intelligent switcher, which only energizes the socket if they have been pre-purchased, reducing the need to distribute live power around the plane.

Most people would really only want a few hours of charging. Then you could have a capped number of active sockets per flight of say 50-100 seats.