My guess is we will get iphone with bigger screen this spring. Apple will not have a 4" phone, which is basically a rehashed version of a phone that was released in 2012 on the market for another full year! They can not afford it, more and more customers will turn to their competiton which offers choice of screen sizes.
They should keep selling 5c as an affordable 4" phone and discontinue 5s in spring replacing it with iphone 6 that would sport 4,5-4,8" screen. Preferably iphone6 should be introduced before next Samsung Galaxy phone to steal it's limelight.