Currently, the only feature in the game for sharing cards are the "request deck" feature, or to just see ingame what card people are using.
It would be cool if there was a feature where, just like linking items in MMO's like World of Warcraft for example, you could shift-click a card while typing and it'd put the card in the message you are typing. This way, you will share the card you're putting in where others can then click on the message link and it'll show the card shared.
Additionally, players could right click the shared card link and have options like "search in marketplace".