Valve was always waiting for the moment when Microsoft would be at their weakest, possibly during some kind of transition. They were too early with Steam Machines as a response to Windows 8 but this might be the time. Xbox is faltering and ARM threatens to end Wintel ecosystem. I wouldn’t be quick to applaud those developments though.
We have Google Linux for phones and it looks like we’ll have Valve Linux for gaming PCs. Valve is not your friend so this platform will be gradually locked down, for convenience at first. Then you’ll either use Valve Linux or you’ll be locked out of your games library - obviously not directly but alternatives will be too fiddly for mainstream. This will allow masses to be herded into Valve operated marketplace which was always the point.
The biggest corpo mistake of last century, computing Wild West for mainstream will die bit by bit unless this process is stopped with regulations. It’s ironic that it’s happening with money made from Windows.