You would need to have a Speedway GP championship and a Speedway World Championship, otherwise you would have 2 different World Champions...a bit like boxing. The top riders would have to be banned from league racing anywhere and the World Championship would have to be the premier event. But then who would want to ride GP?. The only answer is to scrap the GP and revert to the World Final route, but speedway has moved on and it won't happen.