This hack was tweaked until the MMC/SD controller in the SoC was happy with it. Other controllers may differ. In any case will you need the ability to switch CMD and CLK to GPIOs (without disabling the entire MMC controller) and to bit-bang them at a reasonable speed (at least a few MHz).
So it's quite platform-dependent in its current shape, but you can probably apply the same principles with other SoCs as well.
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What makes this great (and unusual) is that there's an entire SoC in that FPGA, not just the CPU core. And it's all Open, including the graphics.
This hack was tweaked until the MMC/SD controller in the SoC was happy with it. Other controllers may differ. In any case will you need the ability to switch CMD and CLK to GPIOs (without disabling the entire MMC controller) and to bit-bang them at a reasonable speed (at least a few MHz).
So it's quite platform-dependent in its current shape, but you can probably apply the same principles with other SoCs as well.