Every iPhone came with final version of new iOS release. (beta of iOS6 = June, final version of iOS6 = october = 6th iPhone )
My predictions:
- same structure, thinner, little bit wider
- metal back
- 4", same 3:2 form factor, 1024x768 (>300ppi)
I agree that it looks like an October release and a metal back would be nice. However a 4" 1024x768 (1.333 ratio) display will look ridiculously square on a phone.
The display will look just like the Pantech Pocket here with a 4" 800x600 screen, same ratio:

Also here's the LG Optimus Vu with a 5" 1024x768 screen:

I personally kinda like the square-ish ratio since I think it's more practical for my preference but probably won't work too well for most of the market.