I'd expect the chip appears in lots of Yamaha keyboards because once you have a hardware platform that works the software becomes the major on going cost.

They will upgrade the chip to newer and faster versions but the software and hardware reengineering required to change to a completely new chip would be significant and expensive. They may get forced that way if the chip gets dropped but if Yamaha are a major customer it might be cheaper for them to fund development and continued production rather than changing chipsets even though the amount of CPU power you get these days for little cost is amazing.