Interesting rumour. Firstly because the resolution is 2.5x the current one in each dimension, when the obvious guess would be 2x (2048x1536) for scaling of assets. The end effect is true retina display on the tablet, whereas maybe 2048x1536 might still have had perceptible pixels. I can see why Apple would decide to go for true retina even if it meant a non-perfect scaling of resolution, and oddly enough it adds a bit of credence to the rumour.
Secondly Apple could move to Samsung's 32nm process (or TSMC's 28nm process) from the current 45nm process, and in the process upgrade to an MP4 graphics chip from an MP2 - a doubling of graphical power that would be required for such a display, and keeping games rendering smoothly. There is also the possibility of getting a quad-core CPU too, like NVIDIA's Kal-El Tegra 3.
So it is just the timing that is odd - it's still quite soon after the iPad 2 came out. Possibly the iPad 3 would be the top-end product, with iPad 2s filling out the $499 - $699 price points.