Auto-form filling is cool and helps the situation but what about NON technical individuals who wouldn't understand how to use that or people who don't understand plugins? How about if your purchasing something on a company card vs. a personal card? What if you have multiple cards?
Wouldn't just being able to swipe be a whole lot simpler?
Even if you had a credit card swiper connected to your computer you'd still have to enter the CVV2 and associated address information because from the merchant's point of view it'd still be a card not present transaction. If you want to change that, you'd have to go down the road of having a piece of hardware that a third party can trust the owner hasn't tampered with. That's a really difficult problem as various DRM schemes have shown.
The there's the integration between the swiper and the operating system and the operating system and the browser. And at the end you are still left with a UX very much like the form filling software because the browser needs to guess where to put the information and have some way of fixing it if it got it wrong.
Wouldn't just being able to swipe be a whole lot simpler?