You must be dreaming. Apple is very uncomfortable when the word 'choice' comes up.
But i agree with you, it'd be quite nice of Apple to offer two sizes. But that would require for Apple to realize that not every consumer wants the same size phone year after year.
However, the current 3.5" size I actually very much like in the iPhone. Even though I don't use one, I think the form factor is one of the best on the market. 3.7" is *my* ideal size. I would consider 4" acceptable if and only if it was edge to edge with a minimal bezel. All the gigantic 4.3+ inch android/windows phones that are being released are a nuisance. The only phone thats really impressed me is the HTC One V, but its not available for T-Mobile so it hasnt phased me much.
Not only are the 4.3+ inch phones big and bulky (and a drag to put inside front jean pockets) but THIS particular image should help understand things;
Image
I currently use a 3.8" HTC Glacier (aka MyTouch 4G) and even at its size I find it somewhat bulky.
I think the *perfect* phone size is (total size, not screen or anything) was the Nokia e71; 114mm x 57mm x 10mm