@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.
I can see really two problems with the smart card proposal.
With a smartphone, you can have your home desktop computer act as a server for your phone's app and then it's easy to limit the liability of how much money you can lose if someone steals your phone.
With a smartcard you could do basically the same thing, store the private/public keypairs for some pre-made accounts that you want to spend from along with the reference txOuts, and some software for negotiating/signing tx.
However, in order to make this work, you have to have your own smartcard reader to load it with money, which may or may not be expensive for your average user (or maybe not?).
The other thing is the sneaky merchant problem. Most smart cards are designed to be used with a tap of your wallet, so a screen would basically defeat the point, and a button on the card would be too easy to accidentally activate (or too easy for a thief to use). The only way to completely circumvent that problem is to have something with basically the capabilities (and independent power source) like a smartphone, where the merchant has no direct control over what is sent. Or else a card with a screen, a pinpad, a cancel button and a "lock price" button, which wouldn't be so easy to use one way or the other and isn't available since most banks can just do a chargeback instead.