Yes, it doesn't appear that it will be solved in libffi.  I don't fully understand the need for the work-around because it should gracefully overflow to the stack.  I can't tell if the issue is a problem with arguments passed by value that need to be passed partially in registers and partially in the stack.

But if the work-around is necessary, it is target- and ABI-dependent: the number of arguments passed in registers is target- and ABI-dependent.  Implementing a work-around solely based on x64 ABI is not correct.  The ctypes stgdict.c code needs to define MAX_STRUCT_SIZE based on the target, at least for the targets that experience the problem.