The guitar and Rhodes demos for Melodyne are extremely clean. Little in the way of distortion, pick noises, scrapes, thumps, all those things that can confuse pitch analyzers...

And yes, we use it at the studio, and it's MUCH less easy than the demos make it out.

Do YOU have it yet? How well does it work for you?

But you are right. I hadn't considered that the analyzing could be done in advance with an arranger. Bet you it's at least fifteen years or more before it becomes a reality for arrangers (if ever), though.