I'm not sure why you say that T6 doesn't meet the "specs" for the wing. Both T6 5w40 and T6 15w40 both have printed information stating that they are both JASO MA/MA2 rated and both full synthetic. And that does meet our specs.
The JASO MA/MA2 rating is only a rating for the compatibility of the oil with a wet clutch.
It has no bearing on whether the oil is suitable for a motorcycle ENGINE, only on the suitability of the oil to a motorcycle wet clutch.
A few posters have suggested that T6 is the same old formula as it's always been, and that Shell dropped the gasoline compatibility due to their wanting to not have to spend (read waste) their money to get the gasoline engine rating.
From what I've read over the last several years, from the BITOG forum to quotes and snippets directly from Shell posted on various motorcycle forums, Shell did indeed change the Rotella T6 formula.
They changed (lowered) the amount of ZDDP (Zinc dialkyldithiophosphate) in T6 to make their new formula compliant with the demands of the catalysts on diesel engines.
That loss of ZDDP, which is an anti-wear agent, is apparently to blame for the dropping of the gasoline engine rating of T6 5W-40.
Motorcycle engines are notorious for requiring more anti-wear agents than are automobile gasoline engines.
The high rpm stress of motorcycle engines combined with their high load valve trains necessitates the higher level of ZDDP.
So, for those who are saying T6 is still T6, do a little investigating.
As for me, I tried T6 5W-40 on the 2nd oil change back in 2014, before the change in formula.
I decided to never use it again in my engine after only 2k km.
My transmission started to shift more noisily and clunky once the oil started to shear.
I now only run non synthetic motorcycle oil, JASO MA rated of course.
I go with house brand (Motomaster) from Canadian Tire, 4 stroke 10W-40 motorcycle engine oil.
It's inexpensive (under $6 quart) easy to find, and does the job.
My trans does not clunk and shifts with the click-click smoothness of new oil.
I've used GN4, which also shifts quietly, but is crazy expensive compared to the Canadian Tire stuff.
I've also tried Amsoil full synthetic, but didn't like the clutch operation with the synthetic oil.
Clutch engagement and take up was not as smooth as with a non-synthetic.
Don't put T6 5W-40 up on a pedestal without really researching it.