Okay, let me ask something. For potential newcomers, we have...
Isaac
Incineroar
Skull Kid
Black Shadow
Shadow
Black Knight
Banjo-Kazooie
Steve
Ken
Dixie Kong
Sora
Dante
Rhythm Heaven Rep.
Medusa
Celica
Geno
Dragon Quest Rep.
Many, or all of these have been predicted in the past. Now, who do you think will NOT get in Smash Ultimate at all, whether in the base game or as DLC? I mean we all know in the past some characters were predicted in a Smash game and never got in.
Out of that list....
I feel that Black Shadow won't get in. F Zero is basically dead and Falcon is more than sufficient to rep it in Sakurai's eyes. Plus we still have Falcondorf and not Canondorf.
Celica won't age very well. Echoes was a great game with underwhelming sales that doesn't strongly merit a newcomer, much less one that can't really be an Echo. Corrin's game was a much bigger deal despite its criticism. If any FE unique newcomer gets in, it'll be a TH character.
I don't think Medusa will make the cut. Kid Icarus is already pushing it in regards to content, and although she's a feasible Echo, I don't feel her franchise is going anywhere for quite a while (especially when it's foster father is always busy with Smash), so I can't imagine she'd make it.
Sora has the status, but he's a licensing nightmare due to being co-owned by both Square and Disney. He may be just too much work to pull off.
Dante isn't happening. I just can't see it. His history with Nintendo is minimal, Capcom already has 2 (possibly 3) fighters, and "the guy who made him also made Bayonetta" is a poor argument. He only gets considered because of leaks.
Steve isn't in. Minecon more or less confirmed it, and his moveset potential is pretty minimal. He also has no personality or animations. Hes literally designed to be a blank slate. We already have that: they're called Mii Fighters. Minecraft may get a stage or some other content, but not a fighter.
Why no Xenoblade reps? Elma and Rex place ahead of a lot of these characters.
All of the others are the main characters in contention at the moment. For one reason or another, they all have a fairly solid shot. As for who would be base vs DLC, who really knows?