The idea DIY Perks tried was to place 2 LCDs ontop of each other to increase contrast levels. 

It was suggested a few times by the community to have the 2 LCDs front-to-front to increase light efficiency as opposed to a diffuser between the first and second to unpolarise the light from the first one. 

I believe the main issue for this application would be to make sure that the two panels are aligned to retain the 0.04x0.04mm pixel size. Longevity would also be a concern.

The reason why I'm thinking of that higher resolution is because of colour dithering and PCB printing, where I'd ideally like crisp voxels of the correct size. If one pixel is 10um larger than it should be when printed, it means that the voxel for the subsequent material would be 10um smaller than it should be, giving inaccurate colours / trace widths just because of the material print order.