Cost is one thing, stability another. As stated on a1k, stability goes down a lot if a second RAM chip is on the board. Compatibility with many CF cards breaks with the second RAM chip, so I decided not to add it to any version due to the bad reputation that the product would get.
Did my popularity go down because of that? Really, I don't care, because my popularity would have gone down much more if I had sold instable 4MB versions.
Wait for the ACA500plus. I'm about to finalize all features, and if you're a little technical, you can read a lot of the new features from the register description: