They still have plenty of characters before they start hitting truly obscure/bottom of the barrel.
All of the characters in Smash fall into two categories: The Protagonist of a game, or Recurring Characters in an established series. The only exception is Sheik (Who was originally attached to Zelda). Other characters who break this rule in Sm4sh started out as costumes, and were made into clones late into development.
So, here's a list of over 30 newcomers that could be added in Smash 5, that still follows these rules. I ordered the list by my personal opinion of likelihood per series.
A lot of the ATs could be made into full characters (Samurai Goroh being the front runner of that group, if a new F-Zero game was in development).
From the Mario series: Paper Mario, a Mario enemy (Like Shy Guy, Koopa Troopa, or Goomba), Boo, Toad/Toadette/ Captain Toad.
D.K: Dixie Kong, King K. Rool
Zelda: Goron, Zora, Impa or, Deku. Possibly Vaati, if there's another game with him in it.
Kirby: Gooey/ Waddle Dee
Star Fox: Wolf brought back, Peppy, Slippy.
Pokemon: A ton of Pokemon could be brought in.
Fire Emblem: The new protagonist from the game Fire Emblem: If
Warioware: Waluigi, Ashley, Mona/ Jimmy.
Animal Crossing: Isabella, Tom Nook
Retro: Golf (NES)/ Takamaru, Bubbles, Mach Rider, Lip, Marvelous protagonist,
New series reps: Rhythm Heaven (Tie between Chorus Kids and the Wrestler), Advance Wars (Andy), Professor Layton, Golden Sun, Chibi Robo, Inklings, Sin and Punishment, Dr. Kawashima, Custom Robo, Project S.T.E.A.M, Fossil Fighters, Wave Race, 1080.