I think the bigger question is - Does Canon Even Need to Answer the D4s...
(btw: if naming convention holds up the D4s will not be any significant increase in mp, if any at all, so it is not going to be a 'pro-body' D800 - just improvements Nikon feels worthy of a different model name)
If we look at Canon's current lineup of top tier bodies (1Dx, 5DmkIII, 6D, 70D, T5i) they all outsell their competitors offerings. While Canon surely wants to advance the technology as much as the next brand, it comes down to dollar and cents in the end.. and it is there that Canon continues to hold the lead. So other than bragging rights to some ambiguous scoring service there is actually little reason for Canon to worry about a specific brand or model they already outsell...
Not everyone will agree with this but as for the other argument - DR! - well it is not as significant or as necessary as many believe. By that I mean while a generous range can provide flexibility and creativity in certain situations it is of limited use. A properly or creatively exposed shot can relieve the need for 14 stop post processing as there would be no 'need' for it to begin with. To give an example: If Canon/Nikon/Sony/etc were to develop a sensor that captured every scene with well lit shadows, exaggerated colors, exaggerated contrast, a complete dream like scene with 50-stops of DR, and no more leeway for processing because the sensor has already captured and reproduced everything there is to be seen - people would still complain about the lack of stops they have in post as a must have, must design etc.
Isn't photography the art/science/creativity of capturing light and shadow?? If the scene being captured has shadows you cannot see into with your eye then there is no 'need' to remove the shadows in development/print, actually doing so tends to ruin the feel of the scene most of the time. It is true that there is an interest/intrigue in an image that looks the way you see the world in a dream - where everything is lit by some magical indirect lighting coming from every direction - but as it is not the way we see the world in real life it will always be a method of processing, a fad, an interest that comes and goes.. It is not something a camera manufacturer need redesign their products around. It is simply not something 'needed' to the point that people fret over 1,2,3 stops difference between this model or that brand.
We would all be better served by a sensor that produces noise free images through the ISO range, even if it did not capture any more than 11 stops of DR, and I mean without downsampling, without film-like-grain, and without 3x the post processing.. I personally would not care if Canon ever squeaked out another stop of DR as long as they work towards ISO 100 performance at >6400 ISO...
You clearly don't understand the primary source of noise. It is impossible to have ISO 100 performance at ISO 6400, while still having comparable sensor resolution to sensors of today. "Noise" is a general term that refers to ALL noise in an image. NOT all noise in an image is from the camera's electronics. Noise caused by camera electronics is called read noise, however read noise only affects the deep shadows, and it is generally only present to a relatively significant degree at lower ISO settings. You are also missing the fact that dynamic range is relative to noise. Eliminate noise, and you effectively have infinite dynamic range (or, in the case of a digitized result, you gain the maximum dynamic range up to your bit depth...whatever that may be...14bits/14stops, 16bits/16stops, 1024bits/1024stops.)
The primary source of noise, by a very significant margin, is photon shot noise. This noise is present in the analog image signal itself, and has absolutely NOTHING to do with the camera. The amount of photon shot noise is approximated by SQRT(Signal), so as signal strength drops (which is what happens when you crank up ISO), the ratio of noise to signal increases. Canon cannot fix that. Canon, as well as every other camera and sensor manufacturer on the planet, have absolutely no control over that. You will never have ISO 100 performance at very high ISO settings like ISO 6400. For that matter, even ISO 100 has noise...its less, but noise is always present in every signal, regardless of what the ISO setting is.
Even if Canon reduced megapixel count to 1mp, and greatly increased pixel size, you are STILL not going to have ISO 100 like performance...it'll be a lot better, but it will still be noisy relative to the image size, because the total signal strength at ISO 6400 is still the same, it's just spread out across fewer pixels with larger capacities. Reducing megapixel count is largely no different than downsampling. You gather more photons per pixel...you lose detail (in the case of a 1mp sensor, a LOT of detail), but you have less apparent noise. ISO 100 noise levels drop right along with ISO 6400 noise levels, so even though ISO 6400 is better, ISO 100 is that much better, too! If you take this concept to its ultimate conclusion, you eventually arrive at a one-pixel sensor of infinite size...that would be the only way to actually eliminate noise at all ISO settings...but, it's entirely impractical and implausible.
You MUST make a trade off. More megapixels, more per-pixel noise, fewer megapixels, less per-pixel noise. Doesn't matter if you reduce sensor pixel count, or downsample in post, either way, it's the same tradeoff. Assuming we stick with current technology, we could DOUBLE quantum efficiency for all sensors that have less than 50% (which isn't that many these days, most sensors are 49-51% Q.E. at least now). If we double quantum efficiency, and leave pixel size the same, that only means that ISO 6400 is now as good as ISO 3200. At the same time, ISO 100 got a stop better as well! It is now as good as a native ISO 50 would have been on a sensor with a Q.E. of 50%. Once were at 100% Q.E. (also technically infeasible...at best we could get somewhere around 90% or so with extreme cooling to -80°C), that's it...we cannot improve quantum efficiency any more. ISO 6400, for that sensor resolution, is the best it's going to be without taking some radical departure from standard sensor designs.
Some patents exist, like color splitting filters, as an alternative to color filter arrays. This might get you another half stop or so. So, ISO 6400 might look as good as ISO 2500. Maybe we employ some kind of layered photodiode...its been done in Foveon-type sensors, however its tricky and the impact on noise is minimal in practice. We might gain another half stop...so ISO 6400 now looks like ISO 1600. Back-illuminated sensor design might get us a small fraction of a stop for pixel sizes as big as they are in DSLRs...it wouldn't be worth the added fabrication costs. That about exhausts the extreme measures we could take to improve ISO 6400. Our sensors will now probably cost a good three to four times as much as they did if we employ all of these techniques...all for two stops of ISO improvement. Were still a long, long ways from ISO 6400 looking anything remotely as good as ISO 100, however...and there is still that nagging little fact that every time we improve ISO 6400, we also improve ISO 100. We never actually achieve the goal of normalizing noise at all ISO settings, because anything we do to make ISO 6400 better makes all the other ISO settings better as well.
It doesn't matter what you do, there is no normalizing the noise levels of different ISO settings. There will always be noise, at all ISO settings, and noise will increase as the square root of the signal as ISO is increased, because that's simply how the physics works. It is impossible to have the same levels of noise at all ISO settings. It's a matter of physics, not technology. We can't break the laws of physics. And they are already bent pretty far with current sensor technology...it is nothing short of amazing that we get the kind of IQ we currently do out of small form factor sensors with 1100nm pixels...that is as small as a wavelength of deep infrared light!!
Now, contrary to the issues above with eliminating all noise at all ISO settings, camera manufacturers DO have control over how much noise their electronics generate. They don't have total control, some things are still beyond their control...for example, we cannot completely eliminate dark current noise, but we can reduce it with CDS (Correlated Double Sampling), and we can greatly reduce it even more by cooling sensor circuitry to temperatures well below zero (-80°C is the sweet spot for power vs. dark current reduction). We can reorganize circuitry, move high frequency components into isolated areas on the die, increase parallelism and reduce operating frequency, and probably a whole host of other things that are currently being discovered or have yet to be discovered that give us control over read noise.
By controlling read noise, we reduce the thing that is actually eating away at dynamic range at lower ISO settings. Canon sensors are not limited to 11 stops of DR. Actually, according to some older studies done by I believe Roger Clark of Clarkvision, when we ignore downstream sources of read noise, Canon's current sensors are likely capable of over 15 stops of dynamic range in analog space. That dynamic range is REDUCED by read noise, which includes noise from dark current as well as noise from high frequency components downstream of the sensor. Canon technically has a lot of options when it comes to reducing this source of noise...hence the reason low ISO dynamic range is a highly contentious point with Canon users. Many manufacturers in the CIS industry have started moving past the 11-12 stop "barrier" that used to be the limit throughout the first half or so of the last decade. Several manufacturers are achieving more than 12 stops of DR at ISO 100, and one has achieved over 13 stops of DR at ISO 100. All of them have achieved that by reducing read noise.
So sorry...but Canon cannot eliminate all noise. Simply not possible. Canon CAN reduce the noise their camera electronics are introducing into the low end of the image signal, however that will do little to affect ISO 6400 performance. Even assuming we employ all the best known options for improving literal light sensitivity on the sensor, outside of GREATLY reducing pixel count (by a factor of two or more, which is really just the same as downsampling), we MIGHT get another two stops of noise performance before we hit an impenetrable brick wall. That still leaves us at least four stops away from having ISO 100 performance at ISO 6400. Assuming the trend towards higher megapixel counts continues, that will only continue to diminish performance at ISO 6400, meaning any technological improvements to improve light sensitivity will only restore ISO 6400 noise performance to the level of sensors with fewer megapixels.