My first impressions of Noesis Studio are extremely positive.
But despite this, preprocessors (#IF NOESIS) and other things related to context switching between WPF and Unity remain a very strong inconvenience.
Does Noesis Studio support code behind (ViewModel in MVVM) or are there alternative solutions that can get rid of WPF once and for all?

When using Noesis Studio you won't need to rely on WPF code anymore, just pure Noesis C# (or C++) code for your ViewModels, converters, interactivity and custom controls.
And if you are in Unity, all the classes defined in your Unity project will be available in Noesis Studio, so no need to create different versions of your ViewModels. This is one of the many things we wanted to address when building Noesis Studio.

Just great news