Yes, I have checked Etherten and it is where no man as gone before, but not quite where I want it to be.
The board I want uses the external memory interface (those A8..15 and AD0..7 pins) to communicate with the Wiznet chip. This will of course make the Arduino Ethernet library (almost) useless, but makes the use of the Wiznet chip faster and a lot more versatile. Instead of sending a bit at a time, we can send a byte in half time (since we multiplex address and data).
Plus, with a little outside logic, using the external memory bus allows you to map all sorts of devices. From the top of my mind I can think of:
ADC
DAC
HD44780 compatible LCDs
memory... the memory seems to be the problem as the bus works too fast for smaller (and older) memories, and other memory chips are too big to use with the 15 line bus. However, Graynomad is developing a board with external memory based on the external memory bus, but using memory pages... There's a post about that in the forum.
By the way, for the signal acquisition board/shield, forget the microcontroller ADs and go for something external using SPI or I2C. The reason for this is that this way the signal can have a really small path up to the AD and then it's just the digital signal going through the wires.So there's less interference, and a few more bits of precision to use. The way I see it, getting a 16 bit AD is, in terms of communication, the same as a 10 bit one.