There's no way this thing will be anything but an Xbox-style Steam Machine, just with Xbox's interface at the forefront. I'm sure you'll be able to play your Steam games, technically, but it'll involve a whole hassle where you turn it on, scroll through your apps, select "Go to Windows", wait for Windows to launch, then move your little joystick mouse over to the Steam launcher and click it and then move your joystick mouse cursor over to Big Picture and then click that and then you can finally launch your game properly.
So it'll appeal mostly to people with Xbox libraries. Hopefully it'll have a Blu-ray player, but I'm not sure I'd put real money on that bet. Such a console will exist entirely to discourage them from giving up and going all in on Steam.