The iPhone went retina in the fourth generation; the full-size iPad in the third. Seems like too much to ask for the Mini to do so in its second.
I’m not so sure generations is something Apple waits on to bring about innovation. The iPhone went retina when it became viable for LCD suppliers to manufacture 3.5-inch LCDs with a pixel format of 960×640 at certain quantities and at certain prices. The same logic applies to the iPad. I imagine Apple’s display group pushing LG Display, Samsung, Sharp, etc. toward mass manufacturing the 9.7-inch 2048×1536 LCD. The iPad went retina when they were able to make the retina 9.7. Apple’s products go retina when it is feasible, technically and economically.
Same goes for the iPad mini. When a 7.85-inch 2048×1536 LCD can be manufactured at the quantities Apple needs for the price Apple wants is when Apple will start building retina iPad minis. A retina iPad mini would be perfect and I expect Apple to announce one next year. The competition is already ahead when it comes to the display. Just look at the 8.9-inch Amazon Kindle HD: it sports a pixel format of 1920×1200 and a resolution of 254 ppi. Not that Apple cares what the competition is up to, but to imagine Apple not announcing a retina iPad mini in 2013 seems almost an impossibility.