The problem with using safe standing as the basis of a 30,000 capacity, is how many people would want to stand? There are some supporters who like to stand, but today this is a minority, as most want to sit. If we ever get to the stage where gates are around the 30,000 level a lot of these extra people will be new / casual supporters. Some might want to stand, but personally, I think these new supporters will be used to watching football on TV and will expect a bit of comfort. If all they can do is stand, they may decide to stay at home and continue watching Sky football on their sofas.