This sounds a lot like the 5D HD I've been predicting for months.
Same body, same price-point as the 5D III, but with an upsized and slightly improved 7D sensor. Take your choice: high ISO and frame rate in the 5DIII or high resolution but lower ISOs and frame rate in the 5D HD (high definition). At the same $3,500 price point as the 5DIII, it remains competitive with the D800, but doesn't undercut the 5DIII.
The 5DIII was targeted to event and wedding photographers who need clean images at higher ISOs. They won't be upset when this surfaces.
As for those worried about the ability of "L" lenses to resolve 46 mp, that's the same density as the 7D sensor.