Title is misleading, Gabe isn't promising any new hardware. Valve is poised to release "more information about how we get there and what are the hardware opportunities we see".
It's like when we all waited months to hear Elon Musk explain how, in very vague statements, the hyperloop could maybe work, if everyone (the government) pitched in a hand.
I think it's fair to say it'll be a fairly long road. Dealing with hardware vendors, especially with GPU manufacturers, will be the biggest hurdle, and getting them all to fall in line will take a lot of work.
Even if he announces the "Steambox" tomorrow, without a truly open Linux solution with very broad drivers support it won't mean much to games developers. It'd just be one more platform they'd have to explicitly support, i.e. they'd have to make a Windows version, Mac version, PS version, Xbox version, and finally a Steambox version
