Quote Originally Posted by laura* View Post
There might be a technical reason why 10 speed twist shifters might never be available: With twist shifters, the cable needs to be pulled in a circle with a diameter greater than the handlebar diameter. A decent angular separation between each gear might mean significant cable pull. I think this (and not precision shifting) is why SRAM went with their 1:1 derailleur ratio - and why Shimano, sticking to their 2:1 ratio, has never offered twist shifters.
You clearly know a lot more about this than I will in a good while, but as a minor point, the Shimano Nexus 8-speed hub gear comes with a Shimano twist shifter. This is likely irrelevant as I imagine cable pull for hub gearing is a different animal to a derailleur.