I still think iPhone Pro is most likely. There are two scenarios to think about, both involve future based lineups.
What would the iPhone line up look like in 2018 when they have two full screen OLED devices, at 5.8" and 6.5" respectively. Do they discontinue the 7 design? If so, what do they name them? The iPhone 9 and 9+, and just act like the 2017 OLED extra high cost iPhone didn't happen? Then the following year you'll have another 5.8" OLED update but it happens to be cheaper than the 2017 OLED, because that was a one-off, and now it's the new base $650 iPhone?
If they go the other way, and replace the Plus model with Pro, then they can continue the differentiation as they have, with the 5.8" model being the normal iPhone ($650), and the larger one being the Pro, with additional features. This allows for the numbers to be dropped as well, if wanted.
[doublepost=1503753541][/doublepost]I thought a few months ago that Edition might have been a likely choice as well, but after seeing the 7S redesign (glass, same polished steel sides) compared to the OLED model, they are practically the same, and so I highly doubt it will be called Edition now, since it's basically the same build.