There already is a single standard communication protocol for handling secure NFC communications.
So I'm going to assume you're mixing the term "payment protocol" with "payment processing".
The only difference between one NFC reader and another is software.
The readers have no problem reading any NFC tag presented because the protocol is already standardized.
It's a simple matter of programming to determine which tags are accepted.
This is why an Amex ExpressPay reader won't accept a MasterCard PayPass card. It's not the protocol... it's the tag signature.
Hell, I can read the NFC tag in my Amex card with my S2.
What *most* people want is something simple to use.
Google Wallet is simple enough, but still requires too many steps to use.
Nice for security, but it really saves nothing time wise vs. pulling your credit card out of your wallet.
I was actually referring to the entire process involved in paying via a NFC-enabled device and terminal. Yes, there's a standard NFC communication standard. That's good, but it only goes so far. To argue otherwise is like claiming we don't need TCP/IP because we have Ethernet.
Do you remember back in the 'old days' when 'swiping a credit card' didn't involve reading a magnetic strip? Do you remember the slightly less 'old days' when you had to pay attention to whether or not a particular store even *accepted* credit cards? The days when you were as likely to need cash as you were to be able to use your credit card on a purchase?
That's the stage we're in with NFC, and it doesn't seem to be (visibly) progressing quickly. (At least not in the US.) Most of the stores I've seen that have NFC-capable hardware at the register either don't have it enabled, or only accept one of Visa or MasterCard using NFC.
As sad as it is, Apple's Passbook software will be *easier* for vendors to utilize than NFC because a lot of the NFC-enabled card readers are still only compatible with *either* Visa's or MasterCard's NFC payment processing protocol. Regardless of whether they can physically *read* the card, they can't accept payments with it, except by utilizing the magnetic strip. (Don't ask me why, it seems like a stupid design decision to me.) In contrast, the barcode scanners the vendors already have are (by and large) capable of reading dozens of standardized 1D barcode formats (and often 2D formats as well).
Personally, I hope NFC becomes a realistic possibility for card processing in the near future, but based on adoption rates I've seen, I don't think that will be the case in the US until roughly the iPhone 6 or 6S (2-3 years). When it *does* start to gain momentum, I don't doubt that we'll see NFC in the iPhone. Until then, it is (as Schiller said) a solution looking for a problem.
Passbook, as it stands, should let me get 7 of those annoying 'loyalty cards' off my key ring, and another 2 or 3 out of my wallet. That's a concrete benefit for me. (It certainly wouldn't be enough for me to upgrade to the 5 if it weren't supported on the 4s, but that's not the case, so I'm glad to see it.)
It's easier for me to simply bump my wallet against the reader without taking it out of my pocket vs. using Google Wallet.
I would love it if I could simply tap my phone against a reader and be presented with a PIN screen on my phone without having to launch an app first.
So, an honest question for you...
Since once the NFC terminals can accept more than one card type, you wouldn't be able to just 'bump your wallet' and know which card was being charged, what do you think the normal procedure is going to be? If you still have to pull out the card to bump it, you're not saving much of anything over the magnetic stripe.
I agree with you completely about the tap & PIN interface on the phone. Maybe tap, select card, and PIN though.