The SE could easily be continued as the "budget" iPhone
and the standard 4.7" iPhone could get the X treatment at the premium end, staying at a 4.7" screen. I would be persuaded to buy that 4.7". (I could not with the 6, 7 or 8.) The popularity of the 4.7" iPhone is plenty of justification for Apple and it could be at a premium price just like the 8, 7 and 6 before it. This would be realistic for Apple to do.
Yes, its size. I might be one of those who regrets upgrading to a larger sized iPhone. I'm basically trying to find enough reasons why I shouldn't do so.
I regretted a larger phone and there are plenty of reasons why you shouldn't "upgrade". I had a 5" Sony Xperia Z1 which is about the same size as the iPhone X, with large bezels just to make it worse, on a 24-month contract. 12 months in, I was hating it and 15 months in I saw myself as virtually having a smaller phone the minute I didn't have any penalty with the contract.
I had the Z3 Compact lined up at 15 months. By the time the contract was up the Z5 Compact had come out. In retrospect I should have bought the Z3 Compact at 15 months because of problems with the Z5 that I had bought new but outright as a grey import....
The SE is one of my best phones ever. It could be my favourite with the Z5 Compact as runner-up. (The UI differences between Android and iOS are not big and I had experience with iPads at work. There's not much to understand if you know Android.) I love and enjoy the compact size of the phone every day. Not for a second do I think that I went too cheap. The features are high quality.
The seemingly insignificant but important features take all the pain away, unlike my old phones and even the Z5 Compact which had high specs (on paper, but it was lag city even with 2GB of RAM and after a factory reset set up as a new phone - RAM management is not good in Android).
And iOS 11 is trouble-free! I just installed it on the weekend. It feels like a new phone. No battery life hit, no nothing!