I think the whole reason they are putting this in a DSLR body is an effort to make it reasonably priced. They don't have to worry about developing a body for it, they can just use an existing skeleton. I say somewhere in the $5k-$7k range, you figure it's just a basic DSLR body with a super awesome sensor, subtract the autofocus, high fps, and all the other photo features and it seems perfectly reasonable that it would be somewhere in that range. Also they could just put an EVF on it and take out the mirrors and whatnot. I don't think it will have built-in ND filters, XLR inputs, or an external monitor like the C300 or anything, so I'm sure they can keep the cost fairly reasonable.
So 1DX body, HD-SDI outs, dual Digic 5+, and 4k sensor that does 24fps/30fps/60fps would be awesome. Also I'm sure it'll have some crazy frame rates at 2K, possibly 120fps (which would be sick for slowmo).
There are some people that are going to say $10k+ solely based on the fact that it's "4K," because that number means everything :

It's not going to be better than the C300, the C300 will remain the flagship for now.