You can shoot in monochrome with an EVF camera and get monochrome in the viewfinder, which is very handy. But of course the mono image is derived from a Bayer matrix-filtered original, so there's a degree of tonal compromise involved. (Thus the appeal of the MM!) Unless, that is, you shoot infrared through a filter that cuts off deep enough into the IR spectrum to neutralize the Bayer filters.
-Dave-