As of just a few moments ago, cards are now customizable! The card layout now has an updated design and lets you choose which fields are shown in your cards.
To find this option, click the wrench icon in the upper left for your app, then go to "Layout Options" and find the "Card Layout" tab at the top.
Thanks a lot to everyone who shared feedback on this here - we hope this new functionality will make the card layout even better for you!
/Jacquelyn - Podio