While I plan to buy a 5d3 I don't see what "justifies" the price outside of aggressive business practice. For me, nothing added to it would change my feeling. I've priced products for markets, and I suspect if I had been Canon, I'd have chosen this price too. I priced aggressively. To us consumers, the $3500 seems a shock at first, but I suspect Canon's thinking takes into account:
1. A huge pent up demand that will create strong initial sales. No reason not to milk this and lower the price over time as demand slows -- if it does slow.
2. A sub-$3k price would probably have meant turnover of nearly the entire 5D2 populace, and I don't think they can produce at that level. So, you price a lot of people out at $3500 and give them a 5D2 alternative. That keeps demand at manageable levels that can match profit forecasts. In reality, both products can create images better than what 95% of users need.
So, "justified" doesn't work for me, but I think I understand their motives. We'll agree to disagree, I'll buy the product and we'll both go on our way.
I quoted Benny because that's pretty much my thinking -- as it was when I bought a T2i at half the price (or less) than a 7D two years ago. Obviously, you don't get close to the AF and speed of the 7D with a T2i, but for someone coming back into photography, it was an excellent first DSLR. It gave me a great Canon DSLR education, and I still contend it can take excellent pictures. It also gave me time to acquire some better lenses than I already had with the intent of moving up.
The 5D3 has as much of the 1Dx as I could reasonably need or want. While I'd love to go to the streets with a 1Dx, I can't afford it, and it has far more capability than I need or will ever need. The 5D3, like the Goldilocks porridge, is "just right" for me.
To me, the 5D3 is really most of a 1Dx for a lot less money.