Well, it would be a nice idea to pay them bitcoin but unfortunately --bitcoin is not a centralized currency.
It is a global sport and expected that it is paid with dollars, not in bitcoin but I think there is a possibility that players will buy bitcoin on the prize they win. There are a lot of people who watch this FIFA event and I think it becomes awareness if there is an ad for bitcoin there, like Nike, Adidas, Pepsi, McDo and etc. But the problem is who is going to sponsor the bitcoin name appearing during those marketing ads.
Also, not every people are interested with this technology and we cannot force them to do so. But that's not a period on the chances that those people could still be hooked up. We may try our 'shot' as this industry continues to emerge and be known by more people. At this moment, the idea of OP is far from reality. World cup speaks in general and that covers both countries who are prohibiting and allowing the use of ceyptocurrency. But those participants who are interested may convert a portion of their prize to cryptocurrency IF they are interested. Some people would prefer other type of investments which are less risky. But I'm okay with such tournaments paying fiat because it simply gives freedom to the player whether to invest or not.