A B&W sensor would be great - 4 times the resolution with no Bayer filter, but then you'd HAVE to use color filters at the lens, no color to recover in PP. A changeable sensor module would be a nice feature. High-res, high-sensitivity, B&W, infrared, all in the same camera.
I always used to carry yellow, red, green and orange (in the days when all the Nikon primes used 52mm or 72mm filters). Skies - yellow for natural, red for dramatic. Skin tones and darken lips - green. Foliage - green to brighten. Stone and wood - orange to bring out details of texture. Now the filter sizes are all over the map, except for the pro zooms standard 77mm size.
Are the color filters in PhotoShop as effective in creating BW from color as the color filters were? I haven't experimented - have you?