Possibly, but not likely. It could be part of the S models getting another year of iOS updates over the preceding non-S models. The discontinuation of iOS updated for an S model has only happened once, because of this it is not possible to define a trend.
Always the case. Never install the third major update from the version of iOS that your phone ships with.
Personally I would never go past the second, from painful experience.
I'd have thought it highly unlikely.
Seeing as the iPhone 4S will be four years old this year I can't imagine Apple would wish to continue updating it.
Not only that if iOS 8 performs badly on the device, what's to say iOS 9 will be any different?
When did Tim Cook describe this? Source?
If history is any indication, then no ):
It's more likely to get iOS 9 than iPhone 4 was ever going to get iOS 8, but it's still hard to say.