I'm myself wondering how much use Nouveau will be here. I imagine the approach that Yuzu will take is actually to HLE the entire operating system and implement things on the service level. During the Switch hacking talk at 34c3, they mentioned that there was a service containing the GPU driver. So basically, the idea would be to reverse engineer how the API works and try to implement the GPU on top of it.

At least, this seems like a sane approach to me. It benefits from less of the existing reverse engineering work on NVidia chipsets, BUT it's higher level, which probably means it will be easier to understand and yield better performance in practice, especially since it is going to have to be implemented on top of higher level GPU APIs anyways.