Nothing I can really help with on the original poster's questions, but my mom has a 90's shaft drive bike. It works acceptably. Having put miles on both, chain bikes are much better UNLESS its the very specific case of a rider who rides with a long dress or fancy slacks or something. Even then it seems only well suited to light duty use. Does not feel like its happy going up steep hills, or with any kind of mashing. Specifically I feel a lot of flex in it, and it shifts roughly under any kind of power.

So basically you're getting less weight, more gear range, higher tq limit, more reliable, easier to service, cheaper to manufacture, and of course better parts availability. Funny thing, it took me using a shaft drive bike for me to realize how awesome chains are. People take it for granted but its a really elegant power transfer system. Some early cars even used chains in the drive system and they did fine. Harrier jump jets used chain to direct their ducts. Tons of other mission critical uses I'm sure too. I mean think about how often you break a chain.. long live the chain.