That's probably going to be used very rarely for three reasons that I see:
1. blood is harder to get than eggs (do we slaughter a cow or a pig every time we want to bake?),
2. blood is better left to be used for other delicacies such as spiced raw blood dishes and others of the sort, and
3. blood is less healthful than eggs--lots of living parasites in blood.
Unless one really just wants to try it out, I cannot see too many people being thrilled about substituting blood for eggs.