I had one on my Verizon 5S that worked with ISIS wallet. The NFC part worked great, but it was a poorly made case IMO.
Not sure how big NFC is over in the States, though, so I don't know how likely it would be for them to go with it.
My guess is they'll be looking at the interest for it if/when the iPhone 6 comes with NFC built in.
If there's enough interest, I'm sure they'll come with their own cases or let some select few companies make official Apple NFC cases.
Not sure how big NFC is over in the States, though, so I don't know how likely it would be for them to go with it.