While there's nothing concrete to say "we aren't getting Nintendo characters" as DLC, I don't feel comfortable wagering at all that we will get any Nintendo characters as DLC.
I think anybody thinking we're going to get 3 Nintendo characters after Erdrick/Dragon Quest character is set up for disappointment. In addition, I don't believe we'll get more than one character from any one 3rd party company (for example, Erdrick and Sora/Lloyd Irving and Heihachi)
I also think, when it comes to DLC, that people have misinterpreted this whole thing with "Nintendo deciding the DLC". It's already basically been proven that Sakurai reached out to Atlus for Joker, which goes directly against Nintendo making those decisions. In addition, while Sakurai did tweet something to the effect of "Nintendo chose the characters", I don't actually think there was a list or anything. I did at one point, but I think it was more of the usual. "Here are the only parameters, but otherwise pick what you'd like".
Reggie was also on record, at the Game Awards, saying that Joker is simply a taste of what we can expect. More or less, very few people expected Joker. So...the other DLC packs are going to be like Joker, but they're going to be a Three Houses character, Bandanna Waddle Dee, and a Gen 8 Pokemon? I can't say I can agree with that.
What I do think is likely, is a diverse set of characters that push the limits of "4 packs after Joker". Remember, for Smash 4 Cloud, Corrin, and Bayonetta each had different costumes that represented more than one game or gender option in Corrin's case.
If the rumors are true, an we get both Jokers (somebody theorized that there are two Jokers in a deck, one black and one red, and that FemJoker is the red one. Makes sense to me), we get the Luminary with Erdrick (if that rumor that "leaked" Mementos and Jack Frost with Joker), then we have 3 more options for other characters.
If Sakurai wants to truly go big or go home with this DLC, I think he's going to take a look at multimedia franchises. That doesn't mean that he isn't going to consider options outside of that, but there are some picks I think that are a step above several others. Those are:
Tomb Raider (SE)
Kingdom Hearts (SE & Disney, Y I K E S)
Dragon Quest (SE)
Tekken (Namco)
Tales (Namco)
Devil May Cry (Capcom)
Monster Hunter (Capcom)
Resident Evil (Capcom)
Ace Attorney (Capcom)
Ninja Gaiden (Koei Tecmo)
...and some others, but they're escaping me at the moment.
From this point, narrowing it down, the choices become a bit clearer. This list isn't meant as disrespect to fans of series like Professor Layton, but to be clear: these series branch out to players who may not already buy Nintendo products. If you pick series that are 3rd party but exclusive to Nintendo, you aren't reaching that crowd that hasn't already bought into Nintendo. That's the biggest issue with selecting 3rd parties that "are basically Nintendo". It doesn't reach out to fans that potentially haven't bought a Switch or Smash yet, or perhaps aren't interested in DLC just yet.
As I said before, I only expect one character from each company for DLC. I don't think Square will get another past Erdrick, and I don't foresee Capcom getting more than 1 character if any at all. If you narrow down the choices above to basically 1 per company, you narrow it down from 10, to literally 4 picks outside of Joker.
There's also nothing at the current moment discrediting Microsoft getting a character. There's also nothing straight up stating there is a good chance of a Microsoft character happening. Sure, they're collaborating going forward. But does that mean a Smash newcomer is going to happen? There's no evidence to support that.
Although, the only character that seems to have gotten away unscathed in regards to that is Banjo. But who knows?
Lastly, I don't think there's reason to overly expect a character from a western developer. It hasn't happened yet, and there are still plenty of stellar choices from Japanese devs. I'm not sure how the process works, but these companies aren't all that far from one another in Japan. The communication is likely easier, and the work can likely get done faster. We'll have to wait and see, but as of right now I feel this is the likeliest outcome. Mind you, I loved Banjo Kazooie when I was a kid, and I firmly believe it would be a dream come true for them to make it into Smash. But I think their chances are overrated.
sorry for the wall o' text