Reports are coming from early arrivals at Worlds that there is some confusion about the Visa situation. Specifically you need a transit visa to pass through South Africa to get to Botswana. It doesn't seem to be something that is stopping people getting to Worlds just is causing some confusion at Johannesburg Airport. The Botswana org comm have sent someone to South Africa to help smooth things over.
So if you are going to Worlds be aware of this. Fix it if you can before you leave but if you can't don't panic. It can be sorted at the Airport.