The consensus on the rumor mill is that the 2017 iPhone will break the #, #S cycle as it will be the 10-year anniversary of the first iPhone and that it will have a refreshed looked with many new features. MacRumors already has their iPhone 8 speculation page up:
http://www.macrumors.com/roundup/iphone-8/
I think one of the best critiques of the iPhone 7 I have read so far was that it was more along the lines of an iPhone 6SS.