According to a new report out of Asia, Apple is going to make a change in its iPhones' lifecycles. Up until now, the company sort of emulated Intel's tick-tock model - one year we'd see a new design, and then the next year's models would only feature refined innards, keeping the looks. This has most recently been the case with the iPhone 6s and 6s Plus, of course - keeping the design of the iPhone 6 and iPhone 6 Plus while sporting better hardware on the inside. So you might have expected the iPhone 7 to bring with it a big redesign, but all the rumors and leaks we've seen about it so far...
Source: http://www.gsmarena.com/big_iphone_redesigns_will_only_happen_once_every_three_years_from_now_on_report_claims-news-18540.php