I've got an interesting idea: Samsung usually updates their phones in the Spring, right? What if every Spring, Apple unveils a new larger model?
For instance, this Autumn they would release the iPhone 6, and in the Spring they release the iPhone 6X. It would have a faster processor, and a new feature or two over the iPhone 6. Then in the Autumn, they again update the smaller phone to have essentially the same or slightly better specs than the 6Xbut again, with a smaller screen.
So the iPhone 6 might have an A8, and the iPhone 6X in the Spring would have an A8X and optical image stabilization along with a 128GB size option. Then in the Autumn the iPhone 6S gets the OIS, 128GB size option, and the A9 processor which is nearly the same or slightly faster than the A8X. iPhone 6XS gets an A9X in the Spring, along with another feature like MIMO antenna like the iPad has, AC WIFI, or whatever. Rinse and repeat.
So you end up with smaller iPhone buyers getting the latest and greatest for half a year, and then spec-whores get a giant phone that would compete against the other giant phones from Samsung. Everyone wins, including Apple. Why? Because the iPhone 6X would be priced higher, but would have a somewhat lower volume of units than the main product linehence fewer components. Why is that a good thing? Apple gets to basically put out their test phone for the upcoming model year putting in features that the larger population won't yet see, and they can refine and ramp up production for the mainstream iPhone.
For instance, the 5S was initially constrained due to new components like the TouchID button. If they had put out a 5X the Spring before, they could have slowly ramped up production on a phone that would ship less units, but would still be premium (and priced accordingly). And hopefully they would have worked out the kinks in the manufacturing process of TouchID before the big launch in the Autumn.
So bleeding edgers (who will spend, spend, spend for the fastest and upgrade yearly) get the fanciest iPhone with a giant screen in the Spring, just in time to knock the wind out of Samsung. The other 80% of the population gets a solid phone upgrade in the Autumn, only 6 months later. The only downside is a strategy like this leaves Apple more open to competition in the Autumn, as adversaries can see what type of features they'll be incorporating into their Autumn lineup ahead of time. But perhaps they could still throw in a surprise for the Autumn models. Some that come to mind are a new form factor, improvements in display quality, better Ear Pods, and software-specific features.