If this thing is already doing pixel-binning for 40 half-pixels, wouldn't it be trivial to have it pixel-bin 4x and make a very nice noise-free 10MP image? I'm sure that Digic5+ can handle that...
In the telecom world anyway, having 4 signals to work with and compare makes a huge difference in the quality of the transmission.
The 70D has an mRAW mode with 11Mpix RAW file output - it isn't exactly 2x2 (sub)pixel binning which would lead to rectangular pixels ...
Here the information from the Japanese Canon website:
RAW: 5472×3648 20 MPixel 24 MByte
mRAW: 4104×2736 11,2MPixel 19 MBytehttp://cweb.canon.jp/eos/lineup/70d/feature-highquality.html
The difference in file size doesn't justify using mRAW alone - perhaps DPP runs faster on the 11MPixel files so you can use an older PC for a longer time.
But if RAW stores the real raw information so it might be a better idea to use the full resolution and scale the images down to 10 MPixels afterwards! This is sth. like binning on a irregular way.
EDIT: Or use 5MPix: 2736 x 1824 Pixels - so you got 1 red, 2 green and 1 blue sensor pixel for each image pixel! - same resolution like the first implementation of foveons and real full color image pixels. In some cases probably helpful to get cleaner colors/contrasts with monochromatic light sources or software red filters.