OK, the iPad’s screen is 1024×768 @ 130dpi. Physical dimensions work out to 7.88”x5.91”.
Those same dimensions at 326 ppi would result in 2568×1926 pixels — more than my current 30” Cinema Display (2560×1600).
I can see Apple bumping the resolution on future iPad models, but not that high. I’m not sure anyone would really want the company to do that, even.