> I've had to debug a segfault before only because the inline function implicitly cast its arguments, and it was accessing a non-existent member. If it were a macro it would access the struct member directly, and the compiler would be able to catch that and warn me before runtime.

This is part of Python C API legacy and as I wrote, it's not going to change soon. The minor enhancement that we can do is to inject an assertion when Python is built in debug mode.