It's too expensive for what the system currently delivers.
That's not to say that, from an engineering perspective, it's poor. Far from it. From an engineering perspective it's something of a tour de force. Sony took its fixed lens RX1, a 135mm sized sensor fixed lens camera, and essentially combined it with the E mount to create the α7. In one fell swoop they asserted their leadership in this specific domain over both Canon and Nikon. But that's just in this one particular domain (a pure mirrorless interchangeable lens camera with a 135mm sized sensor).
The digital camera marketplace is far, far larger than this one type camera, with formidable brands that can produce remarkable results no different from what the α7 can produce right now. And therein lies the problem. By the time you add in the high expense of a limited FE lens selection, along with the high cost of the body, you run up against established camera lines with the same size sensor from Canon and Nikon in the same price range. And both Canon and Nikon have bodies (the 6D and D610, respectively) that will be priced competitively against the α7 on the low end, and even the α7R on the high end, and they will produce far more market wins (purchases) than the α7 pair.
This is the challenge that Sony has to face. Sony will have to realize that their success selling this camera against Canon and Nikon will be spotty at best, just like the current α/Minolta mount SLT cameras, especially in the US market. Where they will gain traction with this camera will be Japan and the far east where mirrorless overall has established a considerable foothold. If Sony is in this for the long haul (and I certainly believe they are), then the α7 is the beachhead from which a hard fought future success will probably come.
For Canon and Nikon, Sony's future success will come at their expense. The α7 isn't the camera Canon and Nikon have to fear right now, but the follow-on generations. Every time I read how the α7 is the "full-frame camera for the masses" I laugh. The camera for the masses doesn't start at $1,600 and up, body only. The camera for the masses sells for no more $800 with kit lens (and in many cases a lot less), and will be the equivalent of the NEX 5N, call it a future α5, with a 135mm sized sensor. When Sony releases such a camera, then you'll see a real shakeup in the camera market. And that's the camera I personally will buy for myself.