Errors in this page
Apparently, this page is confusing different chips. It needs to be clarified a bit, and either renamed, or a R5C8xx page made pointing to it.
The following chips *can* be used in a backwards compatible way in the electronic design (as long as you don't need one of the functions), and Lenovo might just do that depending on supplies:
R5C8x1: R5C811, R5C821, R5C841 (one slot).
R5C8x2: R5C812, R5C822, R5C842 (two slots).
The 81 series is the least capable of them, supporting MMC/SD/SDIO cards and MS/MSPRO memory sticks only.
The 82 series adds SmartCard support (no idea what that means).
The 84 series adds ExpressCard (USB-style) and xD picture card support plus two firewire ports. It removes "smartcard support".
My T43 2687-DDU shows a 0822 pci subdevice, but I am at a loss on how the ExpressCard was implemented (it should require a R5C84x, or it is tied directly to one of the three PCIe buses in the MCH).
Probably one cannot really know what Ricoh silcon one has without actually opening the ThinkPad and looking -- whatever shows up on the PCI list depends on which functions are active, and as ExpressCard seems to be implemented the USB way, it might show up as a USB device in the EHCI USB bus when a card is plugged :(