Some weird ‘Nine realms’ and stub QuadricMeshReduction.cpp has been sitting in the source tree since forever.
Could you please actually implement non-Simplygon mesh reduction, preferably using something like GitHub - kmammou/MeshDecimation: Mesh Decimation Tool which is a good and simple BSD library for it.
This would allow anyone to use some of the Simplygon-only features the engine currently has (Hierarchical LODs, etc)