Kenya has been doing this for close to a decade: http://www.economist.com/blogs/economist-explains/2013/05/ec...
Arguably PayPal has done the same thing, but so many people have bad experiences with PayPal there would be a lot of love for a good alternative.
And of course it would lead to more Apple device lock-in. Tim Cook isn't going to hate that idea.
Maybe we should just sell the entire economy and everything in it to Apple and be done with it?