So if the last section of the article is correct that means ApplePay will be compatible with Mastercard PayPass terminals? If this is true it would be really easy to roll out ApplePay as for example in Switzerland most terminals are PayPass ready.
However, POS software is not at all standardized. You'd likely end up rolling out support for one POS platform at a time. They'll have the hardware you need to support ApplePay, but the rest of the work is probably tricky.
tl;dr POS software systems that accept PayPass can change their software to accept ApplePay.
"Once authorized by the user with Touch ID, your app receives a payment token from PassKit. The payment token encapsulates the information needed to complete a payment transaction. It includes a cryptogram, unique to the specific purchase, that can be decrypted with your private key or when the payment information is transmitted to a payment processor’s server that has your private key. Figure 2 illustrates a typical payment flow. First the app checks that it can offer Apple Pay as a payment method. In this example, the app needs the postal code from the selected shipping address to calculate shipping cost and update the total amount due. When the user authorizes payment, your app receives a payment token from the Secure Element, via PassKit. Finally the app calls appropriate APIs in the payment processor SDK to pass the payment information to the payment processor, they process the transaction. "
Pg 4. - The payment flow. You are asking about the payment provider. They need an SDK or API from Apple whether it's a POS terminal, or mobile device. Once they implement it they can theoretically accept payments. But will Apple allow this?