They might add it as one of those, but they have said it will not cost any extra for Prime subscribers.
It’s basically going to be the same concept as a supermarket “buy one get one free” deal. They lose money on the deal, but gain money overall when people pick up extra things in the shop or from people becoming more loyal to their brand.
Amazon hope to get a lot of football fans to sign up, those fans will then see they get free next day deliver and will shop more on Amazon. Amazon can then use that extra cash to fully take over the world.