It has been discussed quite extensively before. The system used by tennis has been tested for badminton. The accuracy level is only about 70%, much lower than tennis due to the shape of the shuttle compared to a ball (so I understood). And it costs USD50k PER court. So, it's not as if BWF did nothing about the problem. Even if the accuracy is good, it's very unaffordable by badminton. Another solution by BWF is to have international linesmen, but it's for addressing partisan line-calls instead of human errors which is more related to our current topic. A lot of people (including myself) are advocating a fast camera for every line, but the logistics may be as simple as we think. I'm pretty sure BWF have considered it because it's the most obvious solution to come to mind. I'm thinking if someone can come up with a very simple solution, he would be a hero. Something like a slightly (very slight) raised platform where it becomes more obvious whether it's in or out (like table tennis!), but I guess there will be some drawbacks to it, like causing harm to players and of course, singles and doubles have different lines. Yeah, I guess it's a pretty dumb suggestion.