Doesn't FBW come with tail strike protection?
I don't think BBD will have problems with a stretched body. It's easier to stretch than shrink anyway, I believe.
The Chinese 919 is taking forever to get going so I'm not sure it's a threat to anyone. Like it or not, Chinese carriers will HAVE TO buy it. I don't think BBD has a gun to anyone's head as far prospective as buyers go.
Willie