While I'm not commenting on whether or not it's designed to play 4k games people in actuality, I believe are looking at this all the wrong way.
The Ps3 and xbox 360 spent years playing games at even 720p 30fps. And even now the xbox one will play at 900 60 or 1080p 30.
People saying a gtx 1080 can barely play 4k based on it struggling to reach 60fps in demanding games. A potential 4k console wouldn't be aiming itself like a PC gamer, an r9 390 can hold 30fps on a game like Doom at ultra. With the majority of games 30fps would be possible with some settings management. Yes, a few games would be too much, but some optimisation tweaking and settings management, and considering games like the witcher on release would drop below 30fps anyway, a console marketed as a 4k gaming machine is perfectly possible to do if Sony or Microsoft want it enough.
No it wouldn't be pretty, yes I'd rather 60fps on everything at 1080. But this is a business. Get a few games running at 4k, slap 4k marketing on everything, build hype, sell consoles.