I think Impa should get in.
But recently, I'm made a theory that
Skull Kid of all things, is pretty likely.
Let's go and look at what Skull Kid has going for him.
+ Was an Assist Trophy in Smash 4, showing he has notable popularity and is on Sakurai's radar
+ Had a major role in Majora's Mask 3D, a game released in the Post Smash 4 and Pre Smash 5 period, yes remakes count
+ Had a minor role in Twilight Princess HD, a game released in the Post Smash 4 and Pre Smash 5 period, yes remakes count
+ Was one of the big characters used to advertise Hyrule Warriors Legends and Hyrules Warriors Complete Edition, yes remakes count
+ Is very popular as a request and a Zelda character and likely did well on the ballot
+ Easy moveset potential and provides a niche that Smash doesn't have yet both on a gameplay and character level
+ Like Toon Link, he has a design that doesn't clash with Breath of the Wild
Only downsides I can think of are...
- Is not from Breath of the Wild
- Is still a fairly minor character in the Zelda Series
- His popularity has taken a hit in recent years (or his supporters are more quiet rather)
I mean... is my logic faulty here?
I know some people may think remakes mean nothing but...
- Gerudo Valley is a stage on the 3DS version. It's based on Ocarina of Time 3D.
- Pokemon Trainer takes his design from Pokemon Fire Red and Leaf Green.
- Pokemon Trainer was likely chosen due to Pokemon Fire Red and Leaf Green.
- Shadow Moses Island takes the design from Metal Gear Solid: The Twin Snakes
I think Skull Kid has a good shot this time guys.