No plans.
It will undoubtedly have a new body, a faster processor, better cameras, stereo speakers, and all sorts of other nice things. But, as someone said earlier, the 3 does everything I want (reading and writing), so I am unlikely to upgrade this time around. I wanted the Retina display, and I got it. I don't think there is much more Apple can do here.
In fact, I am keeping my eye out for the next Nexus 10, which will probably have a better display than the iPad 5's. I doubt I will get it, though, because I am already completely satisfied with the display on the 3 (the first time in my life that I have been satisfied with a computer screen).