I am thinking about picking a 6s up this weekend with Tmobiles $100 deal with iphone 6 trade in. I could care less about the 7 and didn't plan to upgrade at all. But for only $100 seems like its worth for the bump in specs.
I had a 6S for a couple of weeks earlier this month (I have a pair of iPhone 6 phones). I was really impressed by how much more responsive the 6S is than the 6. If we weren't just about to see the iPhone 7 introduced, and if I weren't looking at full price to replace the phones, the 6S would be extremely tempting.