Most people are suggesting either iPhone 8, or simply iPhone.
I thought it was great when they named the iPhone 4 because it made sense. The iPhone 3G was confusing because it was the second generation iPhone (2G) that used third generation (3G) cellular signal. Then the "S" got thrown in there for some reason with no explanation (perhaps "S" for "Speed"?). Then the 4 made so much sense because it was the 4th iPhone. Then came out the iPhone 4S... okay, continuing the same pattern. I insisted the "iPhone 5" was going to be named "iPhone 6" since it was the 6th generation. Alas, we've followed the 3G/3GS, 4/4S, 5/5S, 6/6S naming scheme since then. If they name this new 2016 iPhone as the "iPhone 7" it won't make a lot of sense since it is still the same body style as the 6, but this is the first time they've deviated from their pattern, so who knows.
Like many other people, I somewhat hope they'll switch to just "iPhone" and use the year to differentiate. Or I think it would make sense to go back to naming them based on the generation, making the 2016 iPhone the "iPhone 10" and the 2017 the "iPhone 11" but there's no way they'd do that after abandoning that idea some 6 years ago.