The 2 areas of improvement for GF-5/SN are 1. fuel economy 2. high temperature deposit protetion (TEOST).
Most of your top tier synthetics will already meet the GF-5/SN spec, but they are testing them for fuel economy improvements. I asked Amsoil recently about GF-5 and they said they are field testing their formulations due out this fall. It's been shown in some studies that friction modification wears out after 5-7k miles of use.
There have been no concerns among most automakers with GF-4 oils and wear control. This is why the Seq IVA stayed the same. The Seq IIIG, which Pennzoil is using to advertise Ultra, I believe stayed the same as well.
Engines are lasting longer then they ever have, most of which use the current API GF-4 specification. No one said the API specification is the end all of specs, but it does ensure consistent quality or at least represents a quality level.
Honda & Toyota are moving to 10k mile drain intervals with many of their new cars, using nothing but conventional/syn blend oils.
dexos1 is supposedly somewhere in between GF-5/SN and Mobil 1 in terms of quality level.
Amsoil does deserve a lot of credit for pushing extended drain intervals. They have been promoting ext. drains since 1974. The industry is finally moving in that direction.