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Any examples of code bases using these modern features like co-routines? I'd love to see an example of it being used in real code.

Only Microsoft is using co-routines in production code via UWP.

CppCon 2016: Kenny Kerr & James McNellis “Putting Coroutines to Work with the Windows Runtime"

While it doesn't use coroutines that I know of, the Dolphin emulator[1] generally makes good use of modern C++ features.