The highest point of the ACA500-ACA1232 combo as photographed is 44mm higher than the highest point of the A500 (a bit less than 2 inches).
There have been more complaints on a1k.org about the location of the CF card slots - people were afraid that they'd rip off the card(s) while typing. I can't confirm this, especially because it's hard to reach to the CF card while your middle finger is supposed to be on or near the letter F on the keyboard.
Unfortunately, there can only be one version: Either this tall version ("prototype 2"), or a flat, wide version. I can't even say which one would be cheaper (I'd guess it's a draw), but that sandwich-solution suggested by Crumb is not an option - it would not help anything (width-problem remains), and on top of that, it would make production a lot more complicated.