One of the biggest reasons LCDs are so inefficient is that they block most of the light. Each R/G/B subpixel blocks everything that isn't that colour and turns

One of the biggest reasons LCDs are so inefficient is that they block most of the light. Each R/G/B subpixel blocks everything that isn't that colour and turns it into heat. The polarizer also has to block all the light that is the wrong polarization and turn that into heat. This means that the backlight has to be incredibly bright relative ambient light. So even if you positioned it to harness the power of the sun as a backlight, it'd be a lot dimmer than the ambient sunlight. The reflective LCD in the OP is nice because the sun is behind you instead of shining in your face. TL;DR, you'd end up having to squint your eyes anyway since the display would be much dimmer than the sun you're staring at, unless you rigged up some cardboard so you didn't have to stare into the sun.