My first impulse was to say that it would likely take the computer resources of a large, three-letter government agency to do this. Then I remembered that I have a Roland VG-88 emulator which uses my guitar as a controller to effectively generate the sound any guitar through any amp, speaker, and effects. Not completely true, of course, but what it does do is amazing. So the core technology exists and is in use.

Then I remembered that Roland(?) has a keyboard which takes your voice and turns it into that of a choir--male and/or female, black or white. This is essentially a vocoder taken several levels beyond what has been done previously.

Still not what you're looking for, but in the right direction. Is it possible that somewhere in the works is a vocal emulator similar to the Roland VG? I don't see why not.

If something like this had already existed my musical presentation would have taken an entirely different direction. I'm a decent singer but don't have the voice for the electronic and blues styles I prefer. Instead, I use my electric guitar as my "rock voice." (In fact, you could make a cogent argument that I'm not a guitarist at all, but a singer who had a guitar in his hand when he decided he had something to day . . .)

Bottom line: It doesn't exist now, but I doubt there is any reason why it couldn't before long. Why don't you put a bug in Roland's ear and see what happens? (Now, how do you convince big-name vocalists to provide source samples for the emulator?)

Semi-related factoid: In the late 70s or early 80s someone figured out how to take 78 RPM recordings of Enrico Caruso, correct the frequency curve, and overlay the acoustics of La Scala to hear how he would sound if he was singing today.

"My primary musical instrument is the personal computer."