I work on Apache Arrow, where the C++ parts require C++11 (and we can't go further than this for now because of R compatibility concerns).
Thanks for the datapoint, that's reasonable of course (though I'll note you're using abseil at least through grpc, and abseil is scheduled to remove C++11 support this year: https://abseil.io/blog/20201001-platforms).
We could say that enabling the Python bindings switches the required C++ version to C++14, but that would bring complication for no actual again given that you're not likely to benefit from C++14 features in the header files of a *C* project, are you?
I get your point, and I agree. My argument was to ensure compatibility with more recent standard versions, and Victor already suggested that several versions could be tested. Best H.