>biracial children have a lower probability of organ donation matches, and a drastically lower probability of bone marrow matches.

Sure, but the vast majority of people will never need this in their lifetime. I doubt this alone would make a noticeable dent in life expectancy statistics. (Also we are within a few decades of being able to clone organs anyway.)

On the other hand biracial people are believed to have stronger immune systems and potentially other characteristics ("heterosis").