Rumored details on the functions of this card:
- Card will be able to StreetPass with 3DS' that connect to Nintendo Network
- Single gamer card will come packaged with the Wii U
- You can buy more gamer cards at stores for $5 - $10
- Nintendo might release a family pack containing multiple gamer cards
- Gamer card hardware (?) features a small, low-res LCD screen similar to the GBA.
Take this for what you will, but they are just rumors for now. It does stand to show that Nintendo would be smart to continue StreetPass in some kind of way with the Wii U since StreetPass on the 3DS has already been a great success worldwide.