They don’t need something to do on the iOS side to implement new banks or even card types into Apple Pay.
Even if it’s a whole new type of card (giro) they need to do that on the Apple Pay servers when adding a card to the wallet and not on the phones. The communication between the phones and the terminals stays the same, no matter what type of card is used.
And they added Sweden and Poland without an update. And u don’t need the latest iOS release to use Apple Pay in those countries.
What I want to say is that there is nothing which needs to wait for iOS 12. And tbh there was nothing reported yet which could hint to new cards or countries in iOS, watchOS or macOS Betas yet. Ok, something bout ELV was found in macOS. But this has nothing to do with Apple Pay and new types of cards.
I think they will start Apple Pay as soon as the agreements are made and the technical stuff is ready on all sides - or better to say in the side of the banks cause i don’t think Apple has to do slot to implement a new bank. Not more than giving them information bout an API and test. Or Apple is talking to banks API, but this can be don’t in a few days plus testing, cause the core of Apple Pay and it’s APIs is done.