Oh AFCA!
I think you are wrong! They want to increase their capacity to 33,000. Anyway, a stadium with 50,000 seats wouldn't make sense. They don't have so many fans as a lot of clubs are close to Leverkusen (Monchengladbach, Cologne, Schalke, Dortmund, Bochum, Aachen....). Nevertheless it will be still a fantastic ground.