[NikkiA]

I'm sure this could be done, today, much more elegantly, flexible e-paper is available without being attached to some heavy clunky PCB, and flexible PCBs are easily do-able, you only need a fairly small/simple mcu and power the whole thing by inductive loops. I reckon you could probably get something close to the size/feel of a credit card, if not more bendy/flexible.

(you might even be able to get away with a tiny capacitance to hold enough power to reset the display to a 'back pattern' when it's removed from the inductive loop 'board', depends on the mcu I guess).

A button to update the card shouldn't be needed, you can detect it via whatever NFC you're using.

[jonahss]

I've heard that switching to all of that will add 20-40 seconds of dead time waiting for the display to change, as the NFC transfers power to run the whole procedure. That'd be too long an interaction time with no feedback.

And of course the cost goes way up.