I speculate for there to be atleast 1 franchise newcomer* for each major franchise in Smash like:

Waluigi for Mario
Y. Link** for LoZ
Adeleine(RIP BitF)/Bandana Waddle Dee for Kirby
Another Pokemon (Maybe if Sceptile if Nerf Frog and Charizard becomes playable or a Ghost/Ground/Rock/Poison type rep)
Lady Lyn(RIP PM) for FE

*Smash newcomer
**He doesn't appear in Brawl and 4 so I consider him a SSF2 "newcomer"

Thoughts in bold.

About Y. Link, there are so many suggestions to give Y. Link a Majora's Mask Moveset, so why not make his moveset revolve around his masks with fierce deity being an obvious FS

Edit: Also, Waluigi needs more love. He doesn't even have his own game series and only appeared in Mario Spin-offs. Either Nintendo give him more spotlight or McLeodGaming and SSF2 would be the one to give him such spotlight

Edit2: A thing I thought about Ganondorf for a while now
I'm pretty sure it's difficult to make a Ganon Moveset that satisfies everyone
If they make it Smash Canon, people who hate "Crappy Captain Clone" won't be satisfied
While if they make it more LoZ Canon, people who like the Smash Moveset won't be satisfied
So what if they mix it up a bit?

Make his Neutral-B the Warlock Sword thingy Custom Moveset from Smash Wii U/3DS with an additional sweetspot on Ganon's fist that acts like normal Warlock Punch
Make his Smashes and some Aerials use his Sword but still have the same properties as his Smash Wii U/3DS attacks
Now the only thing missing are his magic attacks thingies, but the only thing I got is the Fully Charged F-Smash creating a magic projectile... I know, that last idea sucks

Thoughts in Blue Bold

Or maybe have two movesets, like Project Ganon.

Thoughts in dark blue.

I really don't want Sceptile. He's not important enough to be playable. With a series like Pokémon that has over 700 playable characters, you have to be picky.

Besides. People only want him because "the cycle must be completed", not on his own merits.

if theres gonna be another pokemon, it better be gengar
I mean, gengar's so cool! just look at it

I need my childhood, Inuyasha for SSF2 Comeback!
( most likely not gonna happen, but hey a man can dream..)

Gen I is overrepresented in Smash, just look at Smash 4's roster: Pikachu, Jiggs, Charizard and Mewtwo: 4 out of the 6 playable Pokémon in Smash 4, leaving zero room to Gen III and Gen V (Gen II not counting because they got Pichu in Melee).
Although if we're getting a Gen III rep, I'd rather have Gardevoir over Sceptile.

My vote is:
Hawlucha
Pangoro
Braxien
Blaziken
Emboar
Zekrom
Darkrai
Gardevoir

Grovyle has the appearance in Mystery Dungeon 2 as a major character with character development, so he'd have a higher chance than the evolved form, albeit VERY slightly.

My personal thoughts on things that could approach in the future:
Waluigi (I have a mighty need.)
Dedede (Not "if," but "when.")
Bandana Dee (Let's get the Returns Quartet in, why not)
Mewtwo (It's Mewtwo, what do you think)
Ice Climbers (Return to me please my babies)
R.O.B. (We got PAC-MAN and Game & Watch, give them their brother)
Anna (Yes, from Fire Emblem. She's the most recurring character and can use everything, not just a sword, so I don't see why not)
Atleast One of the Smash 4 Newcomers (Villager, Wii Fit, Little Mac, those kind of people)
Knock Knock (IT'S KNUCKLES)
Zero (More Mega Man love, yay)
Solid Snack (Tasty)
And YeahJamFury as an Expansion Character

Bold are my notes.

We don't need fan characters like Blade and Blue.
I'm just insulting myself rn.