Having independent viewports is possible today, but Pascal brings an optimization on the table. It can project one scene in 16 different ways, instead of rendering the scene 16 times, just to re-project it differently. This is a huge gain in geometry and bandwidth performance, or should I say, this is a great avoidance of redundant computations.
NVIDIA’s CEO also pointed out that this is hugely useful for VR application because although there are only two viewports, each of them can now be subdivided into sub-viewports with slightly different projections to match the glass lens curvature. This means that VR will be that much accurate, without any performance penalty.
NVIDIA says that the performance savings could be as high as 50% to 60%, and given that VR requires at least 90 frames per second (FPS), any saving could make a huge difference. Maybe relatively few people have 3+ screens, but every single VR user will benefit from Simultaneous Multi-Projection. See it in action: