I think it seems like a good approach would be to have a relatively low MP count fast professional camera aimed at photojournalism, wildlife, sports, event photography, in all those cases you don't really have use of high MP count, and then make a separate high MP count camera for studio and landscape, which does not need to be fast.
I don't see that you could make enough differentiators between a high MP 5Dmk3 and a high MP 1Dxxx to make people by the 1D instead of 5D. With Nikon seemingly coming out with a 36 MP D800 I see it unlikely that 5Dmk3 will be low MP, and with a high MP 5Dmk3, I think it will be hard to sell a next generation 1Ds with the same or similar resolution figure.