I've done a little research on this, and I think the way to go is to use a smartcard with an integral LCD display and at least one button. These are on the market already.
Yes, but my checksum solution achieves the same with only normal super cheap smart cards.
What are the price of these display cards, I couldn't find it?
Smart cards are expensive to produce, so cardholder adoption rates will be disappoint.
Actually normal smartcards cost less than 2$ a piece; buy in bulk and it comes down from even that.
(
http://www.smartcardsupply.com/Content/Cards/ISO7816.htm)
An innovator/BTC promoter could send them to everyone in a city as a stunt for the price of a normal small ad campaign.
From there, usage can spread like a wildfire.
POS terminals are rented out to the largest merchants in town as part of the campaign.
@OP: Smartcard that's lost = lost money = non starter.
This depends entirely on design - I know my pin code, why wouldn't I just know my private key too?
With my BTC smartcard/wallet and my BTC client I am my own bank and card provider.
I can help develop stuff after the 30. of June and I'm an educated programmer.
I will do it for free, but with a small payment I could do it full time.
I don't see this as something that would take long to create a development kit for.