I'm glad a board like this exists. I had just recently got in Falcom games, or more specifically the Ys and Trails games. Only games I've played through so far are Ys VIII (which was my first introduction in the series), Oath in Felganha, and Cold Steel I & II. I plan to try out the Sky (already starting on the Trails in the Sky FC) and Crossbell games before I get my hands on Cold Steel III (boy, do I have too much free time).
But anyways, I'd love to have Adol be in Smash. Rean and Estelle would also be amazing picks, but I kinda feel like Adol has a higher chance since Ys is basically Falcom's flagship franchise. Kinda like how SEGA has Sonic, Capcom has Mega Man, Namco has Pac-Man, etc. Not only that, but the Ys series has quite a bit of legacy behind it too.
In terms of movesets, I can see quite of unique potential that would make Adol standout from your common swordusers. I won't go too deep in details, but the Skill attacks he acquires in Seven, Memories of Celceta, and VIII could be used for his standard Smash Attacks, while the Monstrum abilities could be his Special moves. (Ex. Adol's grappling arm could be his Side Special, and Hawk's wings could be his Aerial Recovery.)
Or perhaps he could aquire the Emelas swords from Ys VI. Perhaps he could swap through them like Byleth does with the Relics, or something similar to the Monster Hunter MC where each weapon has their own set of moves?
There's also the magic bracelets he requires from Oath in Felganha, though one could argue that he would be to similar to Robin and Hero. I could also imagine Adol having the speed of Marth, the flashiness of Meta Knight, and possibly the strength of Link since that's how I always saw him when I played Ys VIII.
Much like everyone else said similarly, the music in Falcom games are highly praised and critically acclaimed. And Ys is no exception. Ys games house some of my favorite video game soundtracks in existance. Right alongside Kirby, Xenoblade, Sonic, Persona, Castlevania. I could imagine Adol having a similar number of tracks with him like Simon and Terry did. A lot of them could just be the music in their original glory.
Some of my personal picks would be like this:
-Ys I:
Theme of Adol
First Step Towards War
Holders of Power
Tower of the Shadow of Death
Dreaming
Final Battle
-Ys II:
Ruins of Moondoria
Ice Ridge of Noltia
Solomon Shrine
Subterranean Canal
Termination
-Ys III/Oath in Felganha:
The Boy Who Had His Wings
Be Careful
Illburn Ruins
Valenstine Castle
Chop!!
The Strongest Foe
-Ys IV (Dawn of Ys/Memories of Celceta):
Burning Sword
In the Fires of Ignition
Tower of Province (A Kiss from Eldeel)
The Morning After the Storm
Seeking the Vanished Mask
Ancient Land
Temple of the Sun
A False God of Causality
-Ys VI:
Mighty Obstacle
Windslash Steps
Mountain Zone
The Ruined City 'Kishgal'
Ernest
-Ys Origin:
Genisis ~ Beyond the Beginning
Scarlet Tempest
Silent Desert
Scars of the Divine Wing
-Ys Seven:
Mother Earth Altago
Vacant Interference
Desert of Despair
Crossing Rage!
Legend of the Five Dragons
Scias
Ancient Disputation
-Ys VIII:
Sunshine Coastline
Deadly Temptation
A Footprint in the Wet Sand
Crimsion Fighter
Gens d'Armes
Next Step Toward the Unknown
Iclucian Dance
Hope Alive
A-to-Z
-Ys IX:
Heart Beat Shaker
Cloaca Maxima
Monstrum Spectrum
Norse Wind
Desert After Tears
Glessing Way
(I didn't list any for V because I haven't personally played the game).
You got a good 50+ tracks that rivals the number Terry has. Some of these could have their own remixes too. I could easily imagine Yoko Shimomoura doing a cover of Iclucian Dance, or ACE+ with Crossing Rage. And why not add some Sky and Cold Steel music like Sophisticated Fight, Silver Will, A Glint of Cold Steel, Tie a Link of Arcus, and Blue Destination.
As for costume alts...instead of generic color skins, why not have Adol wear his outfits from the various games he was in? His default one could be his outfit from VIII, then it could go to I & II (his outfit in VI is basically the same), Oath in Felganha, Seven, Memories of Celceta, his default outfit in IX, his Monstrum form in IX, then his swimsuit DLC outfit from VIII because why not?
Like I said, I'd be more than happy if other Falcom characters like Estelle and Rean got in over Adol, but if we're going by characters that represent the company/have a legacy (which Smash tends to do most of the time)....Adol has a higher chance.
Then again, the chances of Falcom getting any representation in Smash is pretty low. Still, a guy can dream.
) simply slaps HARD. Four-way dream match of Link vs. Cloud vs. Hero (Erdrick) vs. Adol. LET'S GO! Actually... make it a six-way match; throw in Shulk and Marth as well. 
Wait a minute... six... three vs. three... Oh my...
