However many times analysts predict it, a new model, low-cost iPhone isn't going to happen, not ever. Apple will continue to charge a premium for the newer, higher spec, models, they will continue to sell the older, ever-cheaper-to-manufacture models at a lower cost reflecting that cost of manufacture. Anything which costs less than that isn't in the ecosystem.
Look how fast support on iOS is dropped for older models, full priced older models. iOS7 is going to support iPhone 4 and above, with some of the bells and whistles turned off. Apple aren't going to release a phone which can't run their latest OS, if the 4 can barely do it, that's the minimum spec and thus minimum price for a phone they will sell. Since the R&D cost on an iPhone 4 is sunk already, the production line is built and running and the components are getting cheaper, the iPhone 4 represents the cheapest way Apply can pump out a phone with the power of .. the iPhone 4, any new design to the same power would cost more to make as it's a new production line, and wouldn't be able to run iOS8 when that comes out. What would the point of that be?
Show me all the case photos you want, as many articles from analysts you care to quote, the 'low cost' iPhone as a separate product isn't going to happen, ever. Apple aren't going to fragment iOS, their older phones are about as cheap as they can be to have a given amount of performance and they know how to make them. End of story.