Powder, here you would think the longer upturned nose and tail do their work, but I am not so sure.
Longer nose works well but a shorter tail is what you want for powder.
I ride a lot of deep powder here in Japan and it seems to me the key factor in keeping you afloat (apart from profile, rocker etc) is the surface area supporting your weight on the snow.
Thats why pow sticks are longer than other quiver decks.
Float is only one aspect of riding powder, you can get float through surface area but you will still get serious rear leg burn. The trick is to have nose float combined with tail sink, this gives a fun comfortable ride.
The problem I have with the long upturned nose and tail is that because of the high angle the boards surface area in the tip and tail aren't being effectively used to hold your weight above the snow.
The nose should be longer but not necessarily higher, the up turn just needs to take place over a longer distance than normal much like a surfboard.
I took my neversummer SL to japan and it sucked bigtime even though its got the magical rocker that everyone assumes fixes all, it doesnt. It sucked because of its short little stumpy blunted nose.
Look at boat hull design as its a similar concept. To achieve a nice plane on the water in a speed boat they use a long slow curve. You wont see a tug boat hull running big speeds regardless of how much power it has due to the inefficient hull design.
A blunted nose is a tug boat. A long rocker nose is a speed boat.
Everything I have said is in relation to powder design only, for hardpack riding look at race boards for inspiration, they have bugger all nose and tail length.