Whimsey,
It's really too bad the article doesn't actually link to the JAMA tests being referenced. Do you know of any links to the tests?
It seems to be a case of a group of manufacturers wanting enough product protection, versus an oil company not wanting to provide it due to marketing issues. I mean, the Shell rep admits he's not an engineer, & then summarizes his interpretation of the tests. Sorry, but I'll have to side with JAMA on this one.
You're right, GF-3 does allow for the minimum phosphorus amount JAMA wants, but if they approve xW-20 oils now, then the owners of those vehicles will be "stuck" using GF-4 oils when they replace the current specs. (Because you won't have a choice at that point, right? GF-4 will replace GF-3, & all ILSAC-approved xW-20 oils from that point on will have sub-optimal phosphorus levels.)
Keep in mind JAMA said, “that both viscosity and phosphorus content affect timing-chain wear." So lower phosphorus doesn't appear to be a concern for the xW-30 wts.