Compact Flash cards were supposed to give us that ability. They had cameras, wifi cards, GSM data cards. And, they're electronically identical to a PCMCIA card, so functionality wise, anything you can do with PCMCIA (WiMAX, express cards via caddy, SD cards via caddy, etc.) you can, in theory, do with a CF card.

But, their popularity has waned. Too big, really, for putting in a cell phone ... and standalone PDAs are being replaced in the market by smartphone-PDAs. Though, a CF card slot on the back of a Nokia tablet, which blended right in, and allowed you to choose between Nokia manufactured camera, Wifi, WiMAX, GSM/EDGE/HSDPA/HSUPA, and CDMA/EVDO* cards would be rather nice. Then you can pick whichever one suits your personal taste/needs. (and the only one I would say HAS to be on the base integration is the bluetooth radio)

(* ok, nokia says they're out of the CDMA business, so maybe they just provide drivers for a known CDMA CF card vendor)

And there IS still a niche market for CF cards (someone made some industrial sensor cards for detecting chemicals, temperature, etc... sort of like a tri-corder on a library of CF cards) ... with the right drivers, Nokia could capture that market, as well (because the other cf card hosts are vanishing from the market).

I don't expect to see it happen, though. I think CF cards really are going to go the way of the Dodo.

I did recently see that someone made a wifi card that goes into a SD card slot. So, an SD card slot that has the functionality diversity of CF and PCMCIA cards (cameras (sony had one on a memory stick, so why not?), wifi, gsm, cdma, etc.) would be nice.