If SIA want to sell music and videos, they will just be an online store like itunes or Amazon. If they sell only what they have on the plane, the selection will be a bit limited compared with what people can get on the ground. As the article says, the big question is whether people are prepared to pay to download music on the plane. People were not so keen on Connexion by Boeing because of the cost, and big music/video files would cost quite a lot to download in the air.