as long as 5D mark 3 use the same focusing system, we don't need to worry too much about it...
If the 5D mark3 has 21m resolution, good focusing system, broadcast quality video and high ISO capability, then it is not just a D800 killer, D4 killer, most importantly.... it will also be a 1DX killer.
That's the reason why I think 5D mark3 will not break the rule...
That way, both Nikon and Canon can have the most profit and keep the "Good competition environment".