This is similar to the work done in winapi [1], com-imp[2] and my own tangential work on porting VST3 [3] to Rust [4]
I'm really glad MS is doing this. What needs to be a bit clearer to me is how they maintain ABI compatibility under the hood of MSVC for COM interfaces (which uses the vtable layout of an inherited class) and how that's compatible with MinGW/GCC stacks on Windows, mostly what can break it. I got stuck porting VST3 with multiple inheritance, and it was a headache trying to reverse engineer the appropriate struct layouts for COM implementations.
I'm really glad MS is doing this. What needs to be a bit clearer to me is how they maintain ABI compatibility under the hood of MSVC for COM interfaces (which uses the vtable layout of an inherited class) and how that's compatible with MinGW/GCC stacks on Windows, mostly what can break it. I got stuck porting VST3 with multiple inheritance, and it was a headache trying to reverse engineer the appropriate struct layouts for COM implementations.
[1] https://github.com/retep998/winapi-rs/blob/0.3/src/macros.rs
[2] https://github.com/Connicpu/com-impl
[3] https://github.com/steinbergmedia/vst3sdk
[4] https://github.com/m-hilgendorf/cli-host (sorry for the messy code, it was a weekend of hacking away trying to host a VST3 in pure Rust)