It's going to be a tough decision for those on the annual upgrade installment plans.
Option A: Upgrade "for free"
But you have to turn in a perfectly good phone, pay another activation fee, buy a new case, transfer Applecare and Forfeit year of payments for your 6S
Option B: Keep paying for your 6S and Own it
you don't have the "latest" phone and there always is that one gimmick that new models get (but isn't actually properly implemented until the next next gen. Retina, 64bit, TouchID, 3DTouch...)
I think most annual upgraders are used to justifying the replacement but this year just feels so different. I'm sure the iPhone 7 is a solid device but next years iPhone X will be the ultimate iPhone.