Sharp started production of their IGZO screens, ultrathin, energy saving and with incredible colour and resolution (going as high as 4K) just a month ago. IGZO screens used with IGZO specs (not with usual specs as in current iPads) are extremely energy efficient, said to be twice of existing technology and while IGZO screens are already supplied to Apple, they are used as conventional screens subject to more general iPad and iPhone screens, not necessarily as IGZO screens. IGZO delivers more vivid colors, deeper blacks and sharper image overall compared to traditional LCD screens. Sharp's IGZO on smartphones can go as high as 443 pip or TRIPLE the mini's resolution.
Having said that, my opinion is that to fully utilize this incredible technology, Apple needs some time fine-tuning their processors and display technology and specs to the IGZO specs. It surely can't be done in one month and then you need to do wide range of tests before actually moving up to IGZO specs.
I also think that the new specs should appear in all new products, that is in iPhones, iPads and in minis, rather than just in one product. Therefore, iPhone 5S is a primary candidate for IGZO specs, because it's update comes first, maybe in summer 2013 as Apple accelerates the iphone cycle. The new display specs will probably a main feature for upcoming renewal of iOS 7 which I guess will be declared by early summer 2013 as well. In addition to this hardware change, numerous software changes such as releasing new drivers for their display should be finished in matter of 2-3 months if IGZO will, undoubtedly, employed in future generations of iOS hardware.
IGZO screens in which Apple seems to invest, will be one of main features making it different and better compared to Samsung, whose pentile technology for Galaxy line is rapidly becoming obsolete.
Therefore, the new mini should not just have a Retina, but have a full IGZO specs with its great battery life and great colors, but this can't happen this Spring and most probably late Summer 2013. So current mini's will be sold at least until late summer or will be continued to sell alongside new iPad mini since Fall 2013, similar to 4S being sold along with iPhone 5, maybe at slightly lower price to distinguish it from IGZO retina minis.