I believe I predicted this one...
Yamaha have no hardware vocal harmonizers, and their software one is lame. Without the technology already in some product somewhere, it's hard to imagine where Yamaha would find this code...
Yamaha usually prefer to stay 'in-house', leveraging their own technology across product lines, so a deal with competitors like Digitech or TC (who are already signed to Korg) seems unlikely.
Basically, I wouldn't expect to see any significant improvement in a Yamaha vocalizer until there was a successful HARDWARE vocalizer in Yamaha's lineup...