If the design we've seen is the final design, then I think any innovation or fireworks will have to come from within. I don't really see upgrading from a 4s solely for a slightly larger screen.
My guess is that the main hardware features will be LTE, NFC (Passbook), and the usual slew of speed enhancements. The question is, are those hardware features in combination with iOS 6 enough?
We'll see...
LTE and a bigger screen is all I need.