The kneejerk reaction from most of us is probably that Apple saves money by producing last years models more efficiently and introduces one model at a time. Normally, I’d’ve said this. But other rumors also indicate we’re on the cusp of new display technology that could really change things up. If the promises of IGZO are to be believed, we could have retina iPad minis without an increase in bulk and the big iPad can return to its iPad 2 size with retina in tact.
Apple also started stepping away from stainless steel to colored aluminum. Perhaps it would want to wipe the slate clean and only offer a range of colored aluminum products. But if Apple is to make an all new phone with aluminum back, what else could they do to keep the price down? Without the expensive cellular components, the A5 powered touch still starts at $299 and has the slimmest margine of iOS devices. But maybe, just maybe, they could make a $399 unlocked no contract iPhone with modern enough hardware. Currently, the GSM iPhone 4 is sold at $449 unlocked but it’s the two models ago phone. Cost improvements with IGZO displays and the ubiquity of the 32nm A5 SOC could make an iPod Touch like unlocked iPhone more probable.
As carriers would likely fight this thing tooth and nail, it may get some artificial crippling. Maybe not as bad as the Nexus 4 lacking LTE, but maybe a short list of LTE bands not including one of the big two in the US (and no multiple models to make up for it). The goal here would be to capture the european market, where phone subsidies do not exist and a more palatable introductory price on iPhones is very necessary for consumer adoption (low end Android phones do much better there).
Regarding the multiple sizes though… no. just no. Multiple colored backs and carrier models are essentially interchangeable parts (at least at the fab level) but different sizes just to create artificial price tiers isn’t necessary at the 3.5″ vs 4″ level. The new size is standard, 3.5″ will slowly disappear, but like non-retina 3.5″ resources, will always be supported by developers (sometimes I test on the 3.5 non-retina simulator just to save real estate). Apple has traditionally kept fragmentation as low as possible by transitioning rather than permanently forking (see: death of Rossetta and Universal Binaries).