It's been my understanding that the GT500 would be getting a supercharged version of the new 5.0. I could be wrong, but that's what keeps leaking through the grapevine....especially since production on the 5.4 is supposed to hault sometime in the next year.
Either way, I'd welcome Ford putting an aluminum block into the Shelby regardless of whether it's a 5.4 or the new 5.0. Reducing weight on the frontend is paramount to improving that car's performance for the future.