Fluidity. The most important part of the Modern Ninja Gaiden franchise is its focus on the fluidity of its combat. Being able to seamlessly string combos from weapon to weapon to weapon without breaking a combo. The idea that I think Sakurai will focus on that will capture this idea is by making the character weapon swap by use of the Down Special that will either Quick Swap to the next weapon in the sequence will open a weapon menu around him allowing you to choose a direction on the control stick designated to the weapon. Think Shulk but with multiple weapons of death.
This will be the bread and butter of his playstyle. It will allow him to chain attacks on the fly and cycle through a myriad of moves without slowing down his attacks. Now, for the weapons, and oh god are they awesome.
The Dragon Sword:
Haybusa's most trusted weapon and the Hayabusa Clan's most treasured possession. Only the strongest Ninja will be in charge of protecting and using the Dragon Sword. In terms of Smash this is his go to. Quick but not too quick, strong but not too strong, and super easy to use.
The Eclipse Scythe:
This Big Ass blade on a stick is best used for HUGE but slow sweeping attacks and is best used when you have a group of enemies bunched up and are looking to take them all out as quickly as possible. Most interesting thing about this for Smash though is that, well, we don't have a scythe user.
The Falcon's Talons:
The Falcon's Talons basically turns Hayabusa into a more deadly Wolverine, decking him out with triple blade claws attached to his hands and duel blade claws to both of his feet. He's faster and more unpredictable than ever with these and could serve to be an ample amount of unique moveset potential on their own when paired with Hayabusa in Smash.
The Vigoorian Flail:
Let's think of these as Windmills of Death. Basically imagine Thor spinning his hammer at the beginning of Ragnarok except with a whole lot of slicing instead of blunt force trauma and, well, you got these babies. They're basically little mini scythes linked together with a chain like Nanchaku but are used completely different than both. Keep away and defense is the name of the game here. High percentage? Crank out these babies, let them spin, and it's unlikely anyone in the world of Smash would dare to approach you.
Now this is only a taste of what could be. He also has Nunchaku, a set of Dual Katana known as Dragon's Claw and Tiger's Fang, The Lunar Staff, and Kusari-gama, among others and that's without even mentioning his Throwing Daggers, Incendiary Shurikens, and his Lock-On Bow.
Now that we gotten his weapons outta the way, why don't we move onto costumes because hoo boy he could have some awesome ones.
From his Modern Look to his Classic Look, from his Fiend Look to his Knight Look, and even so much more I haven't even touched on from Dead or Alive or Ninja Gaiden 3, Hayabusa has one of the most substantial wardrobe of any character I've ever seen. They could ALL be included with just a little love.