If you look at the demos for the current, monophonic Melodyne, you can see several demos of changing notes mid note on sung stuff, and it is quite believable. I don't see this as a big problem. Plus, if you could copy and paste, or just move notes about (as we were shown), a LOT could be done to vocals.

My only misgiving is whether this technology works as well on more sustaining material, like strings and BV's. Guitars and Rhodes all have VERY defined transients.

Time will tell...