A number of people are asking what this is about, so, here are a few thousand words on that:
(click to enlarge)
Traditional nose, middle of board flat on ground:
Decambered nose, middle of board flat on ground:
What I believe the decambered nose does, is it becomes part of the sidecut when the board is tilted on edge. It works with the sidecut instead of against it. The upward curve of the nose more closely matches the curve of the sidecut and the shape the board assumes when the whole thing is decambered in a carve.
As you can see in this picture, when a board is carving, the nose is engaged in the snow well past the end of the so-called "running length" of the board:
Therefore the upturn of the nose becomes an active part of the sidecut and an active participant in the carve. A traditional nose shape that curves up abruptly will "plow" through the snow because it is trying to turn along the upward curve of the nose - a much tighter arc than the rest of the board. A low, decambered nose will "slice" through the snow better because its curve is more inline with the sidecut.
The decambered nose does not result in a huge reduction in effective edge length, because the board is still engaged in the snow along most of its length as we can see here:
However the nose is now "unloaded" and not fighting the sidecut or the forward movement of the board.
Also the decambered nose helps with bumps and imperfections in the snow surface. Any impact to the nose of the board as it is carving will be more abrupt with a traditional nose, because the nose upturn is more vertical and curves up at a tighter radius. The nose has to climb up over the obstacle more quickly, in a shorter length of board travel. This creates a shockwave that travels down the board, compromising edge hold and possibly upsetting the rider. You can imagine an extreme example of a nose that quickly curved up to be perpendicular to the board - something like that could actually stop the board in its tracks. The decambered nose spreads the impact out more gradually, and the whole front of the board has more time to deflect more gently.