Think of the speed gains!
I believe that Antares tried this, and it came out with a bunch of errors. So yes, it has been considered, but right now is not a viable option.
Matt
This is something I am working on right now… 
I will definately be posting when I get a build… so just wait.
like meestaplu said, i tried it. it was a messy job that cost 5 hours of my life. perhaps i’ll try this later again, but at the moment i am happy with the blender performance increase
ans since blender now got it’s own raytracer and GI lamp IMO yafray isnt that much important for std work and testing stuff.