I think it will steadily make its way into most airline cabins.
Despite what was stated above, for example, BA has power in all cabins on the A380, 787, 777-300 and refurbished 777-200 aircraft. One each in First, Club World, World Traveller Plus and in World Traveller there are 2 sockets per row of 3 seats and 3 per row of 4 seats.
So, they are being put in, but as a large capital outlay to install, only as part of new product embodiment, not just a "refresh".