I'm wondering if we might actually see that. Maybe not a re-introduction of the six series, per se, but a K-frame sized, .357 revolver that holds six shots.
If you had asked me five years ago if we would see manufacturers putting the time and money into new revolver designs, I would have emphatically said "no."
Since then we've had the Kimber K6, and Colt has introduced the Cobra and King Cobra lines. They appear to be selling, so maybe Ruger will smell money.
I'm probably going to buy a 3" SP101 in the next year, but it would be super cool if Ruger would introduce a slightly larger version with six shots, a 3" barrel and good sights.