Since I always think of the 5 Series to be aimed towards studio photographers, I find some of the specs rumored to be quite awkward, especially the frame rate and the AF which wouldn't be a BIG bonus over the Mk II for studio photographers.
On the other hand, if Canon really is re-shaping the whole line of cameras (suggested by 1DX and G1X), the 5D Mk III might actually have these rumored specs and be aiming towards enthusiasts who are looking for an high-end camera with a good bit of everything. In this case, another model (say 3D) may be imminent...
You are right, 5D series was meant for studio shooters where AF and fps aren't so important but with latest releases/announcement I think they are re-building product lines (as you suggested).
What I think is that the new 5D will be aimed for those who want to have all features (a little crippled from 1D series) and high image quality - and doesn't need 12 fps, rugedness (& size, weight) of 1D.
They may release a crazy high Mpx camera for landscape/studio shooters. But they want tons of Mpx then they can go for medium format and get 60 Mpx digital back wall (or how it is called).