I don't know how I feel about this. There's a good driving sentiment behind it, but I don't think it's a good idea. I mean, it's not like the models who manage to pass the BMI test are going to be representative of the population as a whole. Also, going by BMI really isn't that great of an idea--you can have a very low BMI and still be healthy, just as you can have a much higher one and still look (and be!) healthy.
Ultimately, I think that the best method would be to judge it on whether the model looks too thin, but that has a whole set of issues in itself. What do you think?