"The work that has gone into Steam Deck’s user interface will soon be available through the desktop client, as a new version of 'Big Picture', the version of Steam that’s meant to be used with a game controller and on a television screen," Valve says in a newly-published booklet for its portable console.
That statement quickly caught the attention of fans on social media, though it's worth noting that Valve has been clear since before the platform launched that the Steam Deck UI was intended to replace Big Picture mode. In the official Steam Deck FAQ, Valve noted "that is what we’re aiming for, though the rollout will happen in stages."
The exciting bit here is that Valve now says this update is coming "soon." (Though you may need to multiply by Valve time.)
Steam's current Big Picture mode basically gives you a console-style interface to use when your PC's connected to a TV. The basic design of the UI has remained the same for years, even as the main desktop Steam interface has continued to evolve, and the Steam Deck UI presents a much more modern version of that concept.
Valve has also recently noted that it's working on "improving the docked experience for Steam Deck with all USB-C hubs and external displays," even as the official dock has been delayed. Those sorts of improvements could tie neatly into a broader update to Big Picture mode.
If you're still waiting for your portable, there's good news. Valve is continuing to accelerate Steam Deck shipments.