This is genius by Mr. Nikon. Let me explain myself:
This move by Nikon is not about a body, but about the whole ecosystem. When you buy a camera, being a P&S, a mirrorless, a DSLR, etc, what the company is getting is the potential to upsell you with accessories, lenses, better bodies, and in Canon's case, mice and calculators.
The ultimate business goal for Canon (or Nikon) is for you to buy all of that from them. Thus they offer a coherent progression: from P&S to Rebels to higher end crops to FF. There are two weak links in the chain. The first is the transition from P&S to a low end DSLR as you are not really invested on a system yet. However, even at that level there are elements to steer your purchase to the ecosystem: similar-looking user interfaces, similar design language, brand recognition, etc. The second weak point is the transition from crop to FF. Here you are already in the ecosystem, but for most the transition probably involves buying some new -expensive lenses-.
In the past few years, mirrorless punched a hole in the first transition. Canon (and Nikon) now had to deal with a third option for people ready to move up form a P&S. The main effect of the mirrorless was not really as much as lost revenue due to lesser sales of Rebels, but lost revenue due to the people they failed to get into the ecosystem. Every person who does not buy a Rebel, will not buy flashes, expensive lenses, and probably won't buy your calculators either. Nikon respoded with the Nikon 1 system. Canon responded recently as well, but with an option that seems overpriced at the moment give what brings to the table. In any case, both Canon and Nikon are acting to plug that hole.
Now back to the D600. This camera is aimed squarely at the second transition. This is Nikon telling folks stuck in the Rebel/60D/7D world because of the high cost of entry into Canon FF, "hey fellows, you want s significant increase in IQ for a cost that is reasonable to you (otherwise you would already gotten a 5DIII)?... here have the D600". This is FF for people who is already invested in photography (enough to spend two grand on a body) but for which 3 grand for an MKIII is beyond of what they want to spend. This people almost by definition is bound to buy accessories, lenses, and even perhaps, at some point move up in the ecosystem and get more expensive bodies. Nikon is taking the market that Canon built via very good, inexpensive rebels, and moving them to their ecosystem. Genius.
In my mind there is also a psychological component to the move: Canon has been hitting us with substantial price increases with every new product. Nikon am sure is playing that card: "look, we care about amateurs that were priced out of the upgrade path by Canon. Hence, you should assume we are nicer fellows to deal with". Some may even think Nikon lenses will be cheaper (not the case AFAIK).
My point with this long rant is that the D600 is a game changer, not from a features standpoint but from a business angle. It should not to be evaluated against the 5DIII (or even the 5DII, which for most people updating from more "modern" crops feels stale and outdated... after all Canon trained us to expect a new Rebel every year and a new XXD every two or so. Two grand for a 5y/o piece of electronics that has already been replaced... yeah right). The D600 should be evaluated against the 7D for those upgrading from Rebels or 60D and has no real competition for those upgrading from a 7D. Granted, the 7D is a spectacular camera beyond IQ (amazing AF, great speed, etc.). But for many, those features are nice to have but are secondary to a better IQ. If the D600 delivers on what it promises, Canon will have to respond the same way it responded to the mirrorless sucking -a perhaps significant- portion of the stream of early-stage upgraders because otherwise they will suffer a significant bleeding at the FF transition.
I, personally, will give Canon about a year to release a budget FF because am invested in the system. I don't need an FF that can track a fly flying towards me, a frame rate fast enough to capture a balloon exploding, or weather sealing tight enough I can take the camera diving. I do want better AF than a Rebel/60D (the 7D AF would do), AFMA, 5 FPS would be plenty, and a significant improvement in IQ over what any of those cameras can deliver. Better noise control at higher ISO levels (at least clean images @ 3200... please?) would be greatly appreciated. I will gladly pay two grand for such camera and promise to eventually buy a 24-70 MKII and whatever will replace the 430EXII. If you come up with a ring-based 100-400 (under 2K of course) I may get that as well. If you release this soon I promise I will even buy the calculator.