I'd be curious to know from people who are fans of the SE (like me) how they rank the following advantages it has in terms of how important each are for them:
1) One-handed usability
2) Pocketable size
3) Price
I think I'd rank them similarly, but it's close. Your point on Reachability is a good one: it feels like a kluge. I look at the current iPhone 8 size, and I find it already reasonably pocketable, but it's difficult to hold. (BTW, I would be using a case as well, as I am not comfortable with the curved edges and the materials and I'd worry about a drop all the time...so it's not just the size of the phone held in the Apple Store.)
I already do some trickery to move the icons on the home screen downwards; I feel OK that I could make that work at least. But UI elements within apps are an issue. For me, this issue (one-handability) is the biggest one. Once you've lost that, then further embiggenings are of less concern. If I've lost that physical capability, then I might as well get something even bigger.
My favorite iPhone ever was my trusty 5c. When I got the SE I was able to add Touch ID, 64-bit chip and Apple Pay, but at the cost of other things. Now I'd be giving up even more:
From 5c to SE:
--Gained Touch ID, Apple Pay, 64 bits. Significantly better camera including slow motion video.
--Lost comfort, weight (I liked that the 5c was just a little heaver in my hand), and grippability. I used my 5c with no case. The plastic wasn't slick, it felt secure in my hand, the corners were curved and the design was clean. Now with my SE I use a case.
From SE to 8-type device:
--Gain (significant) improvements to processor and camera, as well as larger screen area
--Lose one-handedness, even LESS grippable and comfortable (well, more "comfortable" than the 5S but the loss of grippability makes it less psychologically comfortable). Camera bump as well (further requiring a case). Remember when we didn't have to deal with those?
Though the tech is better, I feel I will be a lot less happy than I was with the 5c.
Since so many people are expressing their pie-in-the-sky wishes...I'll say mine would be a 5c with reduced bezels, no Face ID needed (I prefer Touch ID), best camera that can fit in there (I do most of my "important" shooting with my DSLR) and an A13 chip. And a price at $500 would be fine. Lower would be better of course, but I'd be happy at $500.