I've been calling 5" and 6" sizes for years since we first started talking about bezel-free or a reduced bezel iPhone. I liked the bigger display size of the iPhone Plus when I had the 6 Plus for a year but it was just way too physically big. 5" in a smaller form factor is great news for those who want a larger phone experience without the larger phone. I'm also hoping they can lob off some of the forehead and chin so that it's a little shorter as well, but that may be difficult if they make it thinner due to battery issues. However, if they can somehow utilize that new lithium battery tech that is roughly twice the capacity in the same size, then it would be easy. The height of the iPhone is especially a problem on the Plus model, and is readily apparent when comparing to popular Android phablets.
Has anyone heard how that new lithium tech is coming along? I have my doubts many phones will adopt it next year after Samsung's battery problems this year. Best to do extensive testing of anything new! If we get the iPhone 8 or some new name next year with a big redesign, Apple may wait a couple years for the next design update for the battery because then they could make the iPhone absolutely razor thin with no change in battery life, lol.
I really doubt the new iPhone would be sold in 4.7" sizes along with the others. It just doesn't make sense. They would keep selling the iPhone 7 in 4.7" sizes. Maybe 4.5" with reduced bezels would be close in size to the current iPhone SE? Although I imagine some people would salivate over a 4" iPhone with reduced bezels and forehead/chin. That thing would be tiny!
Lastly, it's odd that only the 5.8" model would get OLED. Wouldn't the battery life improvements benefit all sizes of the device? If they do that, then that must be the differentiating factor for the Plus model that year. Hopefully that means we get dual cameras on the smaller model! I'd rather have dual cameras on the smaller iPhone and just wait for something better like mLED for the display. That being said, I still hate Apple stratifying the iPhone based on size. I'd love a slightly thicker 5" iPhone Pro that has dual cameras, the best display, more RAM, etc. I want the best iPhone without having to compromise on size.