Maybe I'm not picturing all of the possible outcomes, but the way I see it, this Momentum Air Dodge sounds great for closing in space and attacking a person. Here's my scenario:
You're trying to get close to somebody. Now in Melee, you could wavedash towards them, hop over projectiles and stuff, and then from that poin there's shield-grabs, spot-dodges, all sorts of different techniques.
Now from what I've seen with this Momentum Air Dodge, you can throw out a dodge while still carrying out the motion of whatever you were doing. Also by the look of that Mario GIF, you can pretty much continue fighting right after you landed from an Aerial Dodge...where as you used to squat down a bit more.
So couldn't it be possible, as an approach to your opponent, to short hop, then time an Air Dodge just close enough so that your opponent throws out an attack and misses, then you land from the Air Dodge and deliver a counterattack of sorts (strike or grab)?
Secondly, we assume the opponent is expect a short-hopped air dodge, so they choose to wait until you land, then punish you....only you bust out your own attack instead of an air dodge. Now you got them second-guessing themselves. Mindgames.
That's how I'm picturing this Momentum Air Dodging working for the good of the game's depth. Since you can now bust out momentary aerial invincibility, AND you no longer enter a super-vunerable freefall, you can mess with your opponent and get them guessing when you're gonna dodge and when you're gonna attack. Get them to guess wrong, then either punish them immediately, or dodge through their attack, land, and punish them afterwards.
It's like somebody said - It's an aerial spotdodge. It sounds better than a normal spotdoge to me, because you can slightly control the length of time you're in the dodge animation by pressing the dodge button at various distances from the ground.
Edit: I realise what I'm talking about sounds like a Triangle Jump. Actually, it is. Only difference is, in Melee, your air dodge momentum was set, so you had to be at a certain distance to perform that Triangle Jump, and as I said, you ended up squatting. This new Triangle Jump on the other hand is looking to have less lagtime from the landing, so the jumper can attack quicker.
So if I'm right, you can have a pretty lengthy air dodge depending on your character's speed, short hop, and successfully dodge through attacks and counterattack.