I think it would be very nice to have something like that to reduce the burden of implementing COM interfaces. This shows for instance on the windows.gaming.input module a 30% LoC reduction (from ~6800 to ~4700), even though the module already had a boilerplate helper macros already.
The MR introduces macros to automatically implement each IUnknown method, as well as all of them at once. It also includes a helper to implement IInspectable methods at once, as well as macros to forward both interface methods to a base interface or an outer object. Last, it provides higher-level macros to implement a main interface and any number of sub interfaces and generate IUnknown, forwarding and vtables for all of them at once.
It uses widl to generate additional per-interface macros, for things like inheritance and vtable generation. The rest of the macros are otherwise shared in a Wine-specific header.
The implementation is split to show individual macro being used, although they are later replaced by higher-level macros. The individual helpers are still useful in some corner cases where specific behavior needs to be implemented, or for aggregating classes.