I haven't seen any indication of any technology that would go into the next iPhone that would make it significantly different than the current one (except one of course: LTE).

The camera is as good as its gonna get for a while, the screen is as good as its gonna get for a while, I don't predict any increase in storage size, I don't think Apple will abandon the basic "external antenna" design ... the main improvements to my mind are likely to come from software.

This is all idle speculation of course, nobody actually knows at all. At a guess I'd say we have until at least September before we find out.