It did give them time to tweek their marketing approach for sure (focus on weight, F8 AF, etc).
I certainly noticed that Nikon is highlighting the f/8 AF ability. But...I'd be very interested to know exactly how they implemented this. From the published information: "...the D4 maintains the power of the eleven central AF sensors, including one cross-type even if the combined open aperture value is f/8."
Personally, I'm almost positive it's #2. The subsequent statement in their announcement was: "If the combined aperture value is between f/5.6 and f/8, you even have the power of fifteen central AF sensors available, of which nine are cross type sensors." I highly doubt the AF sesnor has individual points of differential sensitivity, such that the center cross point has additional f/8 lines, and the surrounding 8 crosses have additional f/7.1 lines or something like that.
Rather, it sounds like they saw the 1D X announcement with the lack of support for AF, tested the D4 models in development, found that they could get away with implementing f/8 AF for some of the points, slightly-wider-than-f/8 for a few more, and altered the firmware to make those points active with an f/8 lens attached.
But, from a competitive standpoint, matching Nikon's announced and touted f/8 AF capability may be more important...
I disagree with your sentiments above because the time frame between the 1DX being announced publicly and the D4 rumors starting to show up is not enough time to develop, implement and test adding f/8 AF. It will have been there from the very beginning, regardless of how it is implemented, otherwise there would be too much risk for Nikon to have egg on face (remember the 1D3 problems?)
For Nikon, being able to deliver f/8 in the D4 was just about "staying competitive" for people with long lenses and teleconverters, thus it was only a matter of time before it happened.
I believe that Canon has been caught unawares by this and that Canon thought that they could drop f/8 support because there was no threat from the competition.
I think this is going to be a costly mistake for Canon because if using teleconverters with long lenses is how you shoot, then it is now all one way to Nikon.
What might end up happening is a 1DXn within the next 12 months that addresses this issue and this issue alone - that is unless they can pull a rabbit out of the hat between now and general availability of the 1DX.
To look at this another way, Nikon can sell a 2xTC with their 600mm f/4, giving someone a 1200mm lens at f/8 that works on their top of the line DSLR. Canon does not have anything functional to compete with that.
I imagine Nikon folks are grinning quite extensively over this.