The low pixel density of a 18mp FF camera would certainly give it better low ISO capability
If they're resorting to cutting the resolution for the sake of ISO we ought to be sad - for full frame, 18mp doesn't go very far. Newer technology alone should have gotten them most of the way there.
To CR guy: What, exactly, is amazing about a camera that has perhaps nearly 1/8 more resolution and 1/5 to 2/5 more shooting speed over the 1D Mark IV, yet is developed with two extra years? If these astounding (I'm sure) data throughput rates require DUAL Digic V CPUs, either they had better be cramming all sorts of extra data in those 16-18 megapixels or they had better be getting some astounding battery runtime or real-time plenoptic calculations because otherwise it would imply they haven't really gained much ground over the DIGIC IV if this weren't the case for a camera with specs essentially unchanged from 2009.
A camera with these specs would put less demand on lens resolution than my old T1i - this is not what Canon has been updating its supertelephoto line for, that seems certain.