Bear with me a moment, A ccd/cmos with let's say 8 pixels, has 2 blue pixels, 4 green pixels and 2 red pixels, this requires interpolation to get a colour 8 pixels image, and then you can convert to monochrome but you start with an interpolated image.
While an 8 pixels foveon does not need any interpolation to get the 8 colour pixels, that's why a 3 MP Foveon sensor (Sigma SD10) delivers a picture quality similar to a 6MP Bayer sensor (Nikon D70, Canon 10, and so on)
If you remove the color filter from the CCD/CMOS you have not 4 Green, 2 red and 2 Blues, but 8 greys, and as in the foveon sensor, no interpolation is required.
That's why I think a CCD/CMOS with the color filter removed will deliver a significantly better B&W image compared to the filtered sensor.