So I suppose the two big questions here (since a Cortex A9-based processor, case redesign, and two cameras are pretty certain) are RAM (512MB or 1GB) and storage (whether it'll move from 16/32/64 to 32/64/128). Right?
I think that, IF there's an iPad 3 this September, either of those changes that don't happen this time around will certainly happen then; basically, the iPad 3 will almost certainly have 1 GB of RAM and 32/64/128 storage.
I wonder if at any point Apple will abandon the separate Wifi/3G models and just have 3G models, but at the WiFi model price points. Doubtful, since there's a lot of margin there, but I could see it happening at some point in the future in order to have fewer SKUs and if competition gets tighter.