I think the whole "new universe/worlds" thing has been improperly framed, though I don't necessarily blame any one person.
For Fighter Pass 1, each character came from a game or series that was not in the game previously in a significant way. Persona 5, Dragon Quest, Banjo-Kazooie, Fatal Fury, and Fire Emblem Three Houses all managed this. This also fits with bringing in content that is "new"- even with Three Houses we got a character, stage, and set of music that previously wouldn't have been in the game.
Min Min is more similar to this than different- while ARMS had spirits, an AT, and mii costumes, it did not have a playable character, home stage, or a whole lineup of music. Each game or series that has come into Smash has contribute to this idea- each crossover brought in a lot of "new" content, with each character being directly tied to a particular game.
This is one reason why I could see Pokemon and Xenoblade Chronicles 2 getting content. Their mascot/protagonist isn't playable in Smash, there isn't a stage, and for Pokemon at least, there's no music from Sword & Shield. Xenoblade 2 has music in the game, but there are several great tracks that could still be added.
With Breath of the Wild 2, I find it mostly difficult to talk about it getting a character because, frankly, all we know is that Link, Zelda, and Dry Ganon are in it. We already have Link largely based on BOTW, and I don't think BOTW Zelda is...really in the running. I can't speak for anybody else, it seems like a 3rd version of a character is kinda...I don't know how people would feel about spending $5.99 on that, but that's just me. It's hard for me to support what is essentially "BOTW2 character" when I know nothing about their role, personality, abilities, or anything. The character has to have something to them beyond, "Is from Zelda", but again, that's just me.
In terms of BOTW 2 being a "new world/universe" I don't know that I agree. We already have BOTW, and BOTW2 is a direct sequel. I don't think that means a BOTW2 character is out or something, but it's a difficult thing to speculate when we know next to nothing about how interesting a pick from the game would be beyond, "Is Zelda".
I don't think a lack of a "new world" means a characters chances are dead in the water...I just think certain characters seem to fit the mold of the Challenger Packs better than others, while others seem to fit the mold of a base roster pick better.
There's also the fact that each pick has seemingly looked for new gameplay ideas that only those characters can do. It doesn't necessarily mean it's a gimmick all the time, but they want each pack to stand out (within reason and realizable for Smash), which is why I think that identity and ability might be underrated here. Sakurai did say that they brought new and unique gameplay in each pack, when he was reflecting at the end of Byleth's presentation, and he seemed to want to continue that. With Min Min, I would say it was continued, and I think that's probably going to be a continued focus.
I do think a focus on "new" content will continue, and that's something that has applied to DLC from Ryu to Byleth EXCEPT FOR Corrin, who came with only 2 songs iirc, and Piranha Plant who is a different case altogether.
Lastly, what I always think about with the current structure of Smash presentations and the characters people want is the fact that they're educational in nature with introducing the game/series they come from. When I look at Terry's presentation or even Byleth, it becomes difficult for me to see Sakurai saying to his audience, "What is Super Mario?" or "What is The Legend of Zelda" or "What is Kirby?". That structure doesn't fit those characters as well as well as it does series that are entirely new to Smash or are less well known in nature (For example, Fatal Fury or Fire Emblem). I've seen this rebutted with, "He doesn't have to do that for those characters" but then that's just making something up to fit the narrative, which I don't agree with. I don't think lacking a "new world" discredits a character but it's not hard to see the structure of FP1 and Min Min as not really fitting series with substantial content already.