Although each of the samples in GoWpfDemo is organized as a pair of files, *.XAML and *.XAML.CS, the only real difference from an MVVM-architecture sample is that it constructs and loads the viewmodel in initialization code rather than separately via a binding on Diagram.Model.
If you don’t want a TwoWay Binding on Diagram.Model, you will want to set Diagram.HasDefaultModel to false.