According to rumors, Valve is developing the tools for running Windows games on other platforms.
Corporation Gabe Newell preparing something similar to WINE. WINE is an application that relays some requests Windows API in a POSIX queries. This allows you to run on Mac and Linux program developed exclusively for Windows.
The same applies to games. Run a Windows game to macOS is really possible, and it’s easier to do than it seems. So Valve decided to create their own tool for running games on Linux and Mac.
The mention of the new features found in the Steam settings. There were found items: “enable Steam Play support for games”, “enable Steam Play all games”, “Steam Play will automatically install the tools to ensure interoperability, which will allow to run on your device games that are created for other operating systems.”
The wording is quite clear and talk about the intention of the developer to provide Steam games to a wider audience and, perhaps, promote alternative operating systems.