It makes no sense to use the x86 ABI today. 32-bit processors are not produced anymore (since post Pentium 4/~10 years ago). 64 bit mode is much better and even provides a better 32-bit ABI. The improvement in GCC 5 should be seen as an improvement for legacy software.
As an analogy, seeing it as a "refresh" for the old x86 ABI is like a patient that goes to the doctor and says he cuts his wrists every week and the doctor solution is to give him iron supplements.