We don't know many details of the new FF camera yet, so actually it's too early to argue it should be 3D or 6D.
Well, the original post actually does mention specs (though they could be entirely wrong
30 megapixels, 1D-class body
Dual Digic5 processors for 6 FPS
61-point AF system, major functions same as 1DX
Equipped with flash (or speedlite transmitter)
There's no way that camera would cost less than the 5DIII, since it has all the specs of the 5DIII, dual Digic5, potentially a speedlight transmitter, and its higher MP. If they introduced that camera at $2500, it'd destroy the D800, but it'd also kill the 5DIII.