They know the empirically proven theory: "Moore's law is the observation that, over the history of computing hardware, the number of transistors on integrated circuits doubles approximately every two years. The law is named after Intel co-founder Gordon E. Moore, who described the trend in his 1965 paper. His prediction has proven to be accurate, in part because the law is now used in the semiconductor industry to guide long-term planning and to set targets for research and development."
in 2005 Moore also noted this cannot be sustained indefinitely and we would eventually run into the limitations of physics (in 10-20 years). There are indications from the semiconductor industry that the rate is already slowing to doubling every three years.
Yes, it seems that it is beginning to slow, but given the pixel density of the D800(E), Sony APS-C sensors, and most of all cell phones, it's clear that the technology to produce 60+ MP sensors for FF cameras already exists. The yields are probably too low to be cost-effective for FF sensors at the moment but in time they will be. The lens makers (OEM and 3rd party) would be fools to "wait" for the technology. Better to have the lenses ready when the sensors hit the market. Take a look at the number of Nikkor lenses that were essentially made obsolete by the D800 (all of the ones not on this list: http://nikonrumors.com/2013/04/29/nikon-published-an-updated-list-of-recommended-lenses-for-the-d800e-camera.aspx/) and it makes sense to be ahead of the curve
This is going to create a clear shift in Canon optical signature. Most of the current L primes are already designed for great creamy bokeh rather than great sharpness across the frame. I believe that releasing sharper lenses in the < 85mm range will partly sacrifice the creaminess. The new Nikon 58mm is quite creamy but, case in point, not amazingly sharp. Having great sharpness and creamy bokeh might take an Otus-like optical effort (and size and price).
With that I don't mean to say they're going to have a bad bokeh. Creamy bokeh is not the only possible pleasant bokeh. But it's just going to be different from what people were used to with their 35L, 50L, 85L, etc....