I will put anything you want internal connected to the USB Host, for less than half the price of any SDIO devices, I don't quite get the fascination with expensive flimsy devices in a highly proprietary format.
Anything in particular you where thinking about? If it can be done I will put you a second USB SD card slot inside for storage, then you can use the real SDIO for whatever you like
I only hack around with the hardware, as far as I know the SDIO devices need some software yet.