Valve's Steam Trading Cards haven't been in beta for too long of a time, but the company recently announced its beta is ending on Wednesday, June 26 at 11am PDT. It's a very specific time, and there may be a reason for that. At the end of the post, Valve had the following to say:
Making trading cards available to all Steam users is a step towards an event we think everyone can be excited about.
An event "everyone can be excited about" typically means a sale, and for Valve that's a pretty big event. It's around this time the Steam Summer Sale kicks off, where wallets get emptied faster than you can blink. This isn't an outright confirmation the Summer Sale is kicking off on Wednesday, but there aren't many other things that would fit based on Valve's tease.
As for the Trading Cards, every Steam user can take advantage of the feature when it goes live on Wednesday. Valve is also going to be adding some more games to the supported list that day, instead of its usual Tuesday and Thursday schedule. All current features of the Trading Cards beta are planned for the full launch, however things like the Card Binder and Trade Offers are being delayed. Valve didn't offer any kind of a timetable for those, but expect more information soon.
It's nice to see the Trading Cards getting a full release, especially since it adds yet another addictive element to Steam. And whatever the event is that Valve is planning (please be the Summer Sale), we'll just have to wait a couple more days to find out.