Personally I think Valve is too big to let any of Microsoft's ambitions phase them. Steam is THE place to buy and play games on PC, there's just too much money and support there to see it get marginalized or undercut in any way.

That said, I don't know if making or sponsoring a console is a good move for Valve. I'm really not feeling Big Picture. When you boot a game from it, it still runs in the same inappropriate resolution for your TV. Even when you try basic things, like going to your Steam profile page, it opens it up in a web browser. The default Steam web browser, mind you, not this "first person" browser they're hyping up. Controller support is limited, and I'm not sure sticking with XInput is a good way to differentiate yourself from Microsoft, especially when you have the same buttons listed on the prompts. You also can't run media content from elsewhere on your computer as you would expect a console or really any PC-TV interface to do.

In short, it's a controller-compatible interface... and strangely, nothing else. I can't imagine why they decided it was ready to drop the beta designation.