I think this business can eventually become larger than the iTunes if they execute it well.
I couldnt find any information on whether Apple pay users can use this for online purchases or not. If they do this may be their next move will be to naturally be the Paypal competitor.
"The biggest “surprise” over last 2 months is that Apple has squeezed 15-25bps from the 5-6 participating banks at launch (C, BAC, COF, JPM, Amex and perhaps WFC)."
A unit that is equal to 1/100th of 1%
The US does about $12B in card transactions per day. This means that for every 1% of US transactions it captures, Apple could add ~$80M to the annual revenue which is a very small amount against its $140B revenue. Yes there are international markets, but still this is not done for profits by itself.