Well, we know that wind & smoke can come from a very large variety of things in Melee. Landing, jumping, some B attacks, smash attacks, throwing an item, dodging into the ground, ect, ect. Combine that with Link's posture and it pretty much narrows it down to four things: a jump, dodge into the ground, a land, or a wavedash.
After a bit of investigation I decided that it couldn't be a wavedash because of three (combined) points: the wind animation in the screenshot appeared to be either from a jump or a landing; a wavedash produces no landing-wind animation (which is different from that of the wind animation associated with jumping); and while looking at some video and screenshots for wind/smoke, I found that (unlike Melee) characters in Brawl don't produce any animations for wind/smoke when they jump (only when they land, as well as lots of other things). Even the landfall special (among other things, the dodging into the ground in wavedashing/wavelanding) animation only makes little puffs of smoke, which I didn't think equated to the smoke in the picture and so didn't think it was enough.
But it couldn't be any ol' standard landing because of that odd displacement. So what is it? I know there're some other suggestions about landings, but I didn't think they could fully explain it (why I think they don't explain it below in green). But if I know that wind wasn't from jumping, and it doesn't seem likely to've been from landing, then what is it? It has to be from something. Then it hit me, what if landfall special's animation was changed THAT much? I know it doesn't seem that surprising that these kinds of things could have changed (especially to the future me, aka me when I go back and edit some stuff. he thinks it's more obvious), but it is pretty different if you really look at it. That's the only thing left I can think of. But if that's true then that means, while not necessarily a wavedash, appearently a dodge into the ground still preserves momentum.
The last peice, why I don't think it was a landing animation (other suggestions so far):
Crouch canceling a hit (as red stone said). I just did a little testing and found that CCing a hit does indeed make a blast of wind in Melee, it's also the same wind animation as landing. But judging from how slow those panels move (I looked it up on youtube; I'm guessing the AT is about the same as the original), I don't think the wind animation would still be visible after such a long time since the nearest panel that would've hit him is pretty far away.
DI momentum. Even with a fairly low traction character (Samus), I only got a tiny bit of offset from max DI while falling (about 1/3 of that you see from link in the screenshot). And I really doubt Brawl's Link would have that much less traction than Melee's Samus, so I really doubt momentum from DI was the cause.
Hit momentum. If you were to get hit from something while at high percent, you could recover (move the control stick back and forth) during your flight and land on the ground with plenty of momentum left over to make you slide after producing a cloud. But it doesn't really look like this is the case here at all since Link is near the center of the stage, there's not near enough space for that, plus, I don't think somebody would do that (recover so quickly in the air) in a demo for a screenshot where they'd be doing the most basic of things.
Judging by the factors that make wavedashing possible, I've always thought the most likely factor of whether or not it carries over to Brawl would be the future properties of landfall special (this is along the lines of gnosis's first & second property). That would be the most non-intrusive way to filter out wavedashing. But with pretty much everything else excluded, that screenshot seems to most likely be a bit of sliding from an air dodge. And as for the third property, I've thought of that too, but by taking away that control it would add a little risk to every jump. Though small (varying amounts, depending on the jump speed of the character), I kind of doubt they'd do that, but still, I don't completely rule it out either.
So, while I was pretty much neutral before on wavedashing in Brawl, I think there's a good chance it'll still be there. This is just my conclusion, I know I could be wrong about something or even way off since we don't have a lot of info on Brawl atm; it's just what I came to. However, the more dynamic gameplay that comes out of wavedashing's existence is definitely a big plus, and I hope that if we don't have it in Brawl we have something in it's place to keep spacing and movement just as advanced, integral, & important in competitive play.
