I would be interested in knowing which will happen first
1) 1D-X begins shipping
2) 5D3 is announced
My suspicion (and hope) is that the 5D3 will be a D800 competitor and will therefore be around 30 MP. I just can't see Canon letting the D800 go essentially unchallenged. Unless they cripple the AF, a 5D3 with the same sensor as the 1D-X and the AF of the 7D would cause a lot of people to seriously consider whether the 1D-X is worth twice the price. I know I would be one of them.
This has been discussed before but here it is again... at the MP levels we are today; does it really matter a whole lot? you will find most people preferring a clean High ISO 18mp sensor to a regular/noisy 30mp sensor. So with that being a toss, the rest of the features on the 1dx should be able to make the purchase justifiable over the 5d3 at 2x the price.