I think Apple - with iOS 7's finer, wispier typography and all - knows they shouldn't go another year without it.
It's on all the shipping iPhones, it's on the iPod touch
and it's on the full-size iPad. I can't imagine the mini going another full year without it.
Not now, with all the above factored in.
As much as people have complained about, or wanted it, this past year...I can't imagine Apple saying "nope" for another entire cycle. People would absolutely freak.
Something like that, they'd want standardized across the line. Both for bragging rights/marketing reasons, and, more importantly, so everything just looks as good as it can for the user. No "jaggies" or fuzziness anywhere. Sharp, crisp displays across all shipping iOS devices. Now more than ever, with iOS 7.
It's the Macs where I think the ongoing delays will be (I don't even want to think what a 27" Retina panel costs).
I didn't fully understand or buy into the Retina Display hype/mania at first. But after having a Retina-based device for three years now, I can definitely appreciate the difference (and improvement) whenever I use an iPad 2, Mac mini or a pre-4 iPhone. It's subtle, but it's real.