Different from SDIO I presume?
Toshiba FlashAir only mentions being able to read from the card when inserted in a digital camera. Same with EyeFi but Flucard seems to support some P2P receive mode. The control is done with manipulation of "picture files", definitly an ad-hoc hack.
Yeah my understanding is the cards are intended to sync pictures to a PC and when the card is full they delete old pictures that have already been synced. No device will expect the card to change in real time, so before making changes it will have to simulate the card being ejected.
They are expensive because they are aimed at professional photographers, they use them for instant previews on large monitors in a studio. They aren't that new, just rare because of the cost.
It's entirely possible that they are generic enough to work with any type of file.
I would imagine that you'll be able to get remote access to the card from your PC eventually anyway.