No one has confirmed a release date yet.
^^
They haven't mentioned anything new about it lately... they indicated it would become available on Linux eventually.
When the steam box is opened, unless it was already open, I'm not sure
It seems unlikely most players will use a steambox for CSGO without a PC, though that might not be entirely accurate.
They develop Steam OS which runs on Linux, but the main game isn't available there.
It looks like Valve likely distributes their titles across Linux platforms.
Gabe shared on Reddit that things are still happening, but he can't guarantee a date.