As of now, there is no further word on what this entails for Steam users, but people are considering the following:
1) A trading card game?
-Plausible but quite unlikely. It says “Trading Card” not “Trading Card Game”.
2)Trade unplayed games that have been activated in your account. (Over-optimistic)
Nothing much is known about this upcoming feature yet, but as its name implies its going to be somewhat trade-related. Interesting stuff 😀
It is mostly centered around pimping out your profile page. Oh wells.