I can change to BlueprintType and build but when I try to use the interface-specific macros instead of GENERATED_BODY() I get linker error somehow involving the UMyInterface constructor:
1>MyInterface.gen.cpp.obj : error LNK2019: unresolved external symbol "public: __cdecl UMyInterface::UMyInterface(class FObjectInitializer const &)" (??0UMyInterface@@QEAA@AEBVFObjectInitializer@@@Z) referenced in function "void __cdecl InternalConstructor<class UMyInterface>(class FObjectInitializer const &)" (??$InternalConstructor@VUMyInterface@@@@YAXAEBVFObjectInitializer@@@Z)
1>D:\Unreal Projects\TestInterface\Binaries\Win64\UE4Editor-TestInterface.dll : fatal error LNK1120: 1 unresolved externals
I think that I will provide a default implementation for now because I’m not sure a simple log message is worth a lot of time and trouble.