Well according to rumours and speculations with future iPhones, They will continue to increase in size, As for the iPhone 7. Rumours tend to be correct and as a result, people will purchase an iPhone regardless.
If the iPhone 7, not the 6s/plus, had 2 additional larger scaled phones, would you consider purchasing one? Many people prefer larger phones, it seems to be a thing now days, what are your thoughts?
All you need to do is look to current Android phones.
It wasn't that long ago that Apple marketing was spouting about the "perfect" size of the iPhone 5 (https://www.youtube.com/watch?v=O99m7lebirE). Once they saw how well the "non-nonsensically" large Android phones were doing, they cannot wait to jump on the bandwagon. Typing suggestions? Third party keyboards? Notification actions? Widgets? Battery Stats? The list goes on.
All the features that have been available on Android for years - never has stopped Apple from constantly claiming that "this changes everything".