Not very long ago I posted a piece on the theoretical resolution of lenses, and it's not as simple as some might believe. The actual maxima depends on the colour because of the wavelength of light.
Of greater importance is the resolution at the borders and the corners. On the current 5D MkII lenses like the 17 - 40mm f/4 L have virtually no resolution in the corners wide open at 17mm. When images are reduced in size the resolution across the image is reduced and the effect can be very noticeable. On a camera with fewer MP (such as the D3) this effect is no where near as noticeable because the difference between the centres & the borders is less. The solution would be a complete new lens mount with a larger image circle, or perhaps a different sensor shape, square perhaps, or even circular. We are still being driven by the legacy of 35mm film Leica has broken the mould with the S2, but I somehow doubt that many Canon users would be pleased if their precious lens collections was suddenly obsolete. (I wouldn't!)
As for replacement of lenses it's never going to be a perfect solution, no matter how good a lens is physics dictate that the corners will never be as good as the centre, the question each individual has to decide on is how good does it need to be for you to say it's good enough?