I call bullshit on it being capable of good 4K gaming, seeing as it takes a $500 R9 Fury or GTX 980 Ti to play at 4K on a desktop, and even then you'll have to settle for middling settings in the most demanding games. I like the idea of upgrades, though, but it'd be better if they used discrete video cards like a PC, so peeps don't have to buy a whole new console to get the benefit.
PS - I also call bullshit on their "$399" VR. It makes a nice press quote, I guess, but it's not so cheap when you add in the cost of the required camera and move controllers.