I'm most excited about the iPhone 6. Hopefully we'll get a larger screen, maybe 4.3" with an overall wider design. I was very disappointed that the iPhone 5 was just the 4s with a longer screen. I expect the 5s, due out shortly, will be the regular 5 with perhaps more internal memory and NFC. But Apple could offer both the 5/5s for folks who love the current dimensions (there are plenty of folks who love it just as it is) and the 6 with a much larger screen for folks like me.
I agree, I think that if we see another device, it will most likely by a "5S" type of upgrade. I also doubt we will see a wider form factor any time soon. As far as NFC, I think we will eventually see an implementation by Apple complete with a funny name for it