All 68040 I a have seen are 5V and are hardobtainium. And when a 3.3V (=less pcb, less cost) 75 EUR, 68060 is available. It doesn't make sense to wad into the 5V swamp.
SDRAM is reasonable effort, but DDR2 is a pain to get working due impedance match, risetime considerations etc.. So rather more sdram chips than ddr modules that will proberbly be more unreliable for electronics hoppyists.
If using PPC is a design decision, Xilinx Virtex is proberbly the most optimal solution (fgpa + cpu in one chop
package)
To get SATA, I have not found any SATA PHY (physcial interface for fpga. So PCI interface seems the most sensible. Possible with a PCI<->Amiga hw translator.
ATX size doesn't imply uggly design per se. You can fit a small board within a larger A4000 case.
Sockets might work on <10MHz Minimig v1.1, but on a >25 MHz A4000 it's deep water. It will distort the signals and hinder any serious performance. SMD soldering is just a fact of life in modern highspeed electronics.
The Coldfire CPU is incompatible in a way that makes it messy to use, Better spend that energy on a m68k verilog/vhdl clone. Which will free a chip and associated support circuitry.
We'r not trying to say it's impossible Just that some issues will have to be resolved before it can continue. And that some choices are more realistic than others.
