I tried it once back in 1982. *Naborr son to *Naborr daughter. Neither parent had bite issues but he had a horrible overbite. We gelded him as a yearling and he is a well loved -now 33 year old. He had a really terrific show career with the folks who own him. Because of the severe overbite and me worrying about his future, I had a buy back clause on him and actually bought him back two times when his owners lost interest in horses before getting him with his forever home in 1991.
It was with those people he was shown and in fact they wound up buying horse property so they could have him at home.
This year a client of mine purchased a Ganges daughter specifically to breed to my Ganges son. The breeder of the mare and my stallion encouraged that breeding. The mare did get in foal but with twins and wound up slipping the pregnancy early on so we will re-breed her next year (mare owner did not want to re breed immediately as the summers are too hot in her opinion to have a foal). It will be interesting to see what we get.
So although I have not been brave enough to do half sibling to half sibling again with my own horses (though I might try it again one day), I do not object to it and have no issues having