You'll have to forgive the ramblings of an old designer, waking on too much coffee after sleeping on too much rum. I want to talk a little about how fashion often wins out over function (in many things, but for our purposes, snowboard design).
A long time ago, a few innovative chaps decided to take surfing to the mountains. They rode predominantly powder, and surfed the mountain the way you'd surf a wave. Because the snow was deep, and these people were influenced by surfing, the boards looked a lot like surfboards. And they turned like surfboards too.
However, as snowboarders migrated to packed surfaces, it quickly became evident that "surf shapes" (convex outline) don't work. In fact they can be downright scary if the board has no concave outline anywhere through the tail.
Snowboarding also quickly became skateboard influenced, rather than surf influenced, and as such snowboards began to resemble more closely a snow skate rather than a snow surf. This was partly due to the appeal of skate tricking your way down the mountain as a style, and the simple practical necessity of having two wide points on each end and a narrow wait so the boards would turn and hold an edge through the turn.
While a wider nose and narrower tail, with the waist being the narrowest of all, is going to enter corners faster, the skate influence meant that quickly snowboards became true Twin Tip shapes. The symmetrical twin tip had arrived, and was here to stay.
No matter what, right?
The problem is that a wide nose, up in the tip, is the wrong shape for powder. Watch films of powder riding on twin tips. The rider is angling the board up to get the nose to ride over the powder, meaning that the board doesn't really engage the snow until its close to your front foot. This means that the point of initial contact is almost the narrowest part of the board, and much narrower than the wide tail, making for a "slow entry" into turns, resulting in you having to force the board through the turn. You might not notice that you are, but you are.
Image A shows the board the way the rider is running trim in the image above. Image AA is thus effectively your design. A narrower point of entry than exit to the sidecut. Or backwards tapering.
Now lets shift the board back on itself from the Blue (original) to the Orange (shifted), along with the inserts, so your front foot is in the same place relative to the wide point of the board. Now chop the back of the board off where the twin tip ended, and extend the nose (yellow) to where the blue twin tip originally began.
Or you can extend it less... this is why you'll often hear people say that you can ride a directional shape shorter than a twin - because you're simply not extending the nose as far out to match your blue starting point.
Voila, all of a sudden you have a variable displacement dedicated powder board. The long nose can be rockered up gradually as you have the "time" to not need an abrupt kick, the outline extends forward gradually so it creates an even and smooth entry into the snow, so when the nose does burry, it wants to evenly and smoothly climb up to the surface, and your sidecut relative to your boots remains essentially the same as what you started with, albeit a shorter tail.
This has its own benefits as it makes the tail slashy, which in powder is a whole lot of fun, and most importantly, with a shape like this, while completely unsuited for park riding, is going to behave much like a normal sidecut board on groomer runs (barring of course a long flapping nose that does nothing for you other than slap the snow as you chatter across machine worked ice cookies)
So why do twin tips persist in being popular for powder, even with people who'll spend the entire day in only powder (or their only time on groomer is to get to the powder). There are a lot of reasons, not the least of which is "it's what I know". A lot is fashion. Women still wear heels despite them not being practical shoes. Walking in them is awkward, but you learn how and you make it work. Like a twin tip in powder, and especially if you've never felt how a directional board feels in powder, you have no reference point.
And of course, because most people ride powder inbounds, and as such they do have to ride groomer to get around to each powder stash. But this is why shapes range from the Wooden decked board above, to the boards below - your shift away from twin tips is dependent on your ratio of groomer to powder. The more groomer you're on, the more your boards effective edge is going to be longer and the nose shortened compared to my line drawing C (or the wood board above).
Clearly this starts to take us back to the surf shapes that the first pioneers were playing with in the 1970's. The closer you get to a surfboard, with the wide point either close to your front foot, or even between your feet, the more the board is going to handle like a surfboard in powder, BUT, the less you're able to ride the board on hard pack.
Surf shapes are as wrong in their entire concept on groomer in much the same way that twin tips are wrong for powder, with one discernible difference: You can ride a true twin in powder if you're willing to manhandle it, you cannot ride a true tip to tail convex (reverse sidecut) outline board on groomer, at all.
Even this board below, which at first glance appears to be a true surf shape, has just a little sidecut in the rear third to make it "possible" to at least get down groomers.
Directional boards are here to stay, and most people are probably going to end up on something that resembles more a directional Twin like the one below, than a surf inspired shape above (and eventually, something more between the two). Swallowtails, moon tails and all this allow you to fine tune the general concept, but are not in and of their own major design components in the overall discussion.
This is because inbounds, on mostly groomer and hard pack environments, boards like the one below are perfectly adequate for performance based riding on hard pack, can be taken into the park for some jibbing fun, and also offer a degree of shape and volume displacement tweaking towards a more effective powder riding arrangement with a drawn out nose, sloping rocker and back shifted outline than a true twin.
Now, where is my coffee?