Hi,
triggered by the proposal and discussions on the forum to add a combined SIM/SD-Reader for another internal Micro-SD card (which I find a nice idea):
I have checked the mechanical fit - and there is no problem to add such a piece.
For the electrical/logical interface, I have analysed all the TRMs and data sheets for understanding the limitations of the SDIO controllers of the OMAP5 [2].
We have no problems running one internal eMMC, one bootable high-speed SD slot, a second non-bootable standard speed SD slot and WLAN.
But we have a problem to interface a third Micro-SD slot because the SDIO5 port is n/a on the 5432 chip.
Options to solve this are
* replace the eMMC by the Micro-SD (which will have a much lower speed limit!)
* interface WLAN though SPI (is not optimal for 802.11n) and use the SDIO3 port
* interface WLAN through (internal) HS-USB (likely to draw more power and needs different chipset/module) and use the SDIO3 port
* interface the Micro-SD slot (or even the second full speed) slot though USB (needs a probably power hungry SD-USB controller chip like [1])