It'll be interesting if the rumors of Apple Pay for web are correct[1]. One could see a near future where using mobile Safari, iPhone users could login and pay at any website just with the credentials stored in Apple Pay + Keychain and the use of their thumbs. I'm sure something similar could be built for Chrome on Android with Android Pay.
1) http://recode.net/2016/03/23/apple-pay-coming-to-mobile-webs...