The Game Boy Advance's e-Reader was brought up when discussing card-based amiibos.
Right now, Nintendo's line of Amiibo NFC figures will set you back $12.99 and are relatively nice looking models for the price. But, that doesn't mean that all future Amiibos will be of the same size, cost, or even format, as Nintendo discussed at its latest earnings call that it was working on card-based Amiibos, as well as smaller, cheaper figures.
While speaking about this, the old Game Boy Advance e-Reader cards were brought up. Nintendo lead developer Shigeru Miyamoto additionally discussed a card game in which you can play simply by swiping cards and then using them to record your play history - in a way similar to how many Japanese arcade games work these days. Miyamoto teased, "But I can't talk about that specifically yet, however card games possess the potential to have a new structure with Amiibo."
Miyamoto also talked about the possibility of smaller, cheaper figures than the Smash figurines, and how they could be used in games like Animal Crossing. Miyamoto is apparently pushing teams to come up with non-standard uses of the NFC reader in the Wii U, the results of which they hope to be able to show off next year.
While the Amiibo figures certainly looked great when they were first revealed, the production models were a little less detailed than we thought. I can't imagine smaller and cheaper figures would look very good comparatively, but I can see how they would work in titles such as Pokemon, or, as Miyamoto mentioned, Animal Crossing, which have a lot of collectible content.
As for card-based Amiibos... Pokemon TCG interaction with the Pokemon video games, anyone?