A reference image for something called Steam Trading Cards has been spotted in the Steam database. With no statement from Valve forthcoming it look like we need to start playing the guessing game. That, or Hungry Hungry Hippos.
It could be that Valve are implementing new infrastructure into the Steam client that will support trading card games outside of the game. That could be that cards you bought/found/unlocked in-game would be added to your Steam inventory and then traded with other players outside of the game. An issue with this theory is why is that so different from what is already done with Team Fortress 2’s hats that it would require a new system to be implemented.
Another possibility is that Valve are working on their own trading card game. One akin to Blizzard’s Hearthstone. Maybe it would feature characters from Valve’s various games. While this is possible it just doesn’t seem to fit. I don’t see Valve releasing a game which has you attacking Tidehunter with Gordon’s Crowbar of Silence for 8 damage any time soon.
“As all the feedback is evidence for, this is just the start of a lot more Steam client updates involving both Trading and the Steam Community / Friends list. There are too many good ideas to list, but it's worth calling out a few items we want to address in the next release(s):
Better tools for finding & starting trades
Trading of CD-Keys
Trading of real world currency
More friends lists features, including more tagging
More games hooked up to trading”
It could be that the trading card system is a means to trade CD-keys between one another.
Any ideas because I’m coming up with nothing that seems likely. It needs to be something Valve would be likely to build into Steam and would require a whole new beta program and hunk of code to make work.