Looks like Valve are rolling out a way to play games in beta, or a purpose-built way to do so at any rate. A new button for requesting access to a playtest has appeared over on the store page for the Hearthstone-looking card game Total War: Elysium. It appears to be the first so far, though more may follow.
The change was spotted and posted by SteamDB creator "xPaw". Total War: Elysium's store page now has a "request access" button for playtesting. "Request access and you'll get notified when the developer is ready for more participants," says the new store section. You do need to be logged in to your Steam account to request access.
Playtest builds have been added as a new application type for Steam, according to xPaw. In addition to being a game or demo or DLC, it sounds like developers will now be able to mark store items as a "beta". Don't you start in on the Early Access jokes now.
So far, the button has only been spotted on the store page for Total War: Elysium. It doesn't look like Valve have dropped an official line on the addition, so it's not clear exactly how the system will work for players or developers.
I've requested access to Total War: Elysium just to see what happens, but it looks like xPaw has gotten a proper invite already.
Valve have been adding all sorts of tweaks and features to their storefront via the Steam Labs experiments they've been cooking up. Most recently they added community recommendations to the front page and now recommend which game you should play next from your library. Interestingly, they didn't make mention of the playtest button in their big blog post about the first year and future features for Steam Labs.