To match parity with the .NET projections system, CsWinRT needs to provide a way for libraries to provide implementations of native interfaces for the native wrappers of managed objects. For example, CsWinRT needs to supply 2 implementations of Windows/Microsoft.UI.Xaml.Data.ICustomPropertyProvider (one for .NET objects, one for CCWs that wrap RCWs); however, these types don't exist without running cswinrt to generate a projection.