Are you envisioning cards as widgets that leverage the API of a partner app or are they just re-formatted mobile web views embedded within another app? For example, Uber wouldn't have worked unless they also built all of the payment and user account/rating functionality into an embeddable mobile web view. Once you're there, you might as well support mobile web.
Have you ever tried to read your site on a phone? As soon as I scrolled, a thousand things blocked the content to get me to subscribe or share. I reward that sort of behaviour with an instant close.