Why can't Yamaha retrofit this feature via firmware upgrade for older boards such as S-serie, Tyros-serie.
Theoretically they can. But the question is: Is it economically feasible for Yamaha to do so? The answer probably is no.
With the Tyros series Yamaha "only" fixed bugs and did new features in the new Tyros models. New models came out every three years (with some exceptions) and people bought these costly instruments. I did.
Now with Genos, the situation appears different. The number of players are shrinking and the economy is different. I haven't seen new high-end keyboard models from other vendors as well.
It seems Yamaha have chosen to give the Genos a longer life. By updating the firmware (v 2) even new features have been added. Also packs with new voices and styles have been provided for free. All in all, this makes the Genos an awesome deal.
Personally I love this strategy. The sound is still amazing (best in the market) and the fun of playing has not diminished one bit.
To be clear: I have no insider knowledge. I just interpret what I see happening. I might be completely wrong.
Maarten