Originally Posted by
Bezalel
The Capreo hub goes down to 9T using a standard QR.
And here's a comparison with a standard hub.
Of course I'm not sure how important a 9T cog is to most tandem teams (maybe for a flatland TT tandem).
Photos from Sheldon Brown
Thanks for pointing that out. I misinterpreted the Bikerumor article that is referenced in the OP. It was saying that the X-12 (12mm axle) was the largest it could go while maintaining compatibility with small (9psd) lock rings.
Just FYI, the Capreo setup is 9spd (or less) only and not really a widespread standard adopted by the industry. Meaning, few sources. Since it was intended for small wheel bikes and so few cogs, I can't see it being a factor.
As for as usefulness of 9T or 10T, those would be useful gears for those wishing to use smaller chainrings. Di2 is a primary example, as these setups that can only handle a maximum of 2 drive rings.