Paswordless login actually fits even nicer in mobile.
You can make the email link open as a deep link in the app and continue right where you left. Context switching in the app is minimal and in mobile apps sessions are usually more persistent anyway
I described the way it is currently done on mobile devices but i was thinking about a way to even cut that context switch by letting an app react to an email rather than handling the link scheme.
See http://www.drzon.net/passwordless-login-in-mobile-apps/ for what I mean