I don’t see why not. Of course Sony would have to pay dearly for that exclusivity. It’s not like MS can just switch to Nvidia, it’s true that the Xbone uses intel instructions and the feature-set of AMD/Nvidia GPUs is basically identical for most purposes, but Nvidia doesn’t make integrated SoCs outside of low-end ARM. They don’t even make APUs. So they would need a separate CPU and GPU which increases costs and cooling requirements.
Also Nvidia, being on top of the world with their GPU business, is less willing to play ball on price than AMD, who until very recently was absolutely desperate.