Two corrections: the viewfinder doesn't have 5.76 million pixels but "dots" ie subpixels. It has 1.9 million pixels, 1920x1080 resolution.
The removal of the colour filter array doesn't and physically cannot make the sensor much more sensitive to light. The difference is only 1/2 to 2/3 EV, depending on how much infrared light (which will blur the image) they filter. This is less than one stop..
The Leica Q3 Monochrom is expected to launch soon as a full-frame compact camera with a 60MP black-and-white sensor. A big leak now reveals the design, key specs and a significantly higher price point of the Leica Q3 Monochrom ahead of its official debut.