Just to be clear Mr_Arduino, you want support for sdio
Good point, SDIO is not simple and not supported on many micro-controllers. The SDIO protocol is totally separate from the SPI protocol. Most SD modules/breakouts can't be used with SDIO since only the SPI lines are connected.
SDIO should be very fast if implemented correctly since more effort goes into the SDIO controller in an SD card because it is used in most consumer devices, PCs, and Macs.
I plan to change the SdFat architecture so it can be ported to a number of micro-controllers.
I will port SdFat to STM32/SPI first since that should be easy if I start without DMA. An old version of SdFat already has been ported to Maple. Next I will do SPI/DMA.
The STM32 processor used in Maple does not support SDIO so I will likely use the this board http://www.st.com/internet/evalboard/product/252419.jsp. I have several SD breakout boards that bring out all SD lines for SDIO.
The STM32F4 is really fast and I understand it. I will look at SAM3U4E and whatever is used in Due later.