I think your right with the 3rd Gen Prelude being the closest love child from the two. In real life though it would be born in secret for fear of the NSX getting the reputation as a dirty tramp, and the unwanted child would be given away for adoption to a dirty orphanage and raised with a bunch of other unloved and useless cars (also known as the Toyota dealership). Over time though, it would rise against adversity and shine through the pack where it would become known to everyone as the MkIV Supra!
Seriously though, a lil of pops and a lil of ma and thats what you'd get...
We'll take an EK Civic and the last generation of NSX for example
FF + MR = FR
I4 + V6 = I6
Since Honda's aren't fans of boost, they're -Boost...and since we know two negatives make a positive..
-boost and -boost = +boost...therefore, turbo'd!
5 seater + 2 seater = 2 seater with useless back seat
Obviously it gets most of its style (eyes/headlights atleast) genetics from dad, and power genetics from mom, but you get the idea.
I can see it now, one day the Supra will show up on at the NSX's front door step and it will be a mother and child reunion. It'll probably show up drunk at the Civics house later on and beat him up because it'll still be dealing with abondonment issues, but it'll still be beautiful none the less.
Aww. Its so beautiful, I think i'm going to cry.