And that's a fair point on Jigglypuff. I mostly put her where I did because her very late addition into Brawl, going by the order in the data and her absence from the SSE, is at least one instance of her being considered lower priority. And considering the sheer magnitude of characters we have now, I could see her being deemed low priority again. But she's definitely a toss up.
For Mario, Zelda, and Fire Emblem, I'd probably rank them like this. This is, again, assuming there are at least some cuts in the next game, which I believe is a reasonable assumption.
Super Mario:
Mario, Luigi, Peach, Bowser, and Rosalina & Luma, I feel, are all totally safe. I don't see any of them being cut even under a case of fairly substantial cuts, which might go against the grain of public perception with regards to Rosalina. A little bit after them would be Bowser Jr., due to the fact that he and the Koopalings were said by Sakurai to have only just made the cut in Smash 4, implying they were a lower priority. That's not to say Jr. is a clear cut, just that he's slightly more at risk than the aforementioned five.
Then further down we have Daisy and Doctor Mario. There's a historical precedent that clones and semi-clones tend to make up the bulk of cuts, so they'd likely be lower priority. Out of the two, I'd say Daisy is
slightly more likely to return due to her popularity and ease of creation even relative to Doc, whereas Doc has been cut before. Piranha Plant would be last. They were incredibly low priority in Ultimate, having been moved from base game to early adopter DLC, and are from a series with a lot of other higher-priority characters.
Zelda:
Link, Zelda, and Ganondorf are obviously not going anywhere lol. Sheik is likely staying as well, though in a scenario with substantial cuts I
could see her eventually going. But she's likely staying. Sakurai has said in the past that having two Links, one adult and one child, is important to him, but in the context of cuts we don't know
how important it is relative to other potential cuts. Toon Link I would say is more likely to be kept over Young Link when it comes down to it though. By a good amount, too. I really don't see Young Link coming back outside of the nigh-impossible Everyone is Back.
Fire Emblem:
Even in the event of some of the harshest roster cuts known to man, I cannot see Marth, Ike, or Byleth getting cut. In addition, I cannot see us losing all three Awakening characters, as I absolutely think at least one out of Chrom, Lucina, or Robin will be kept. The question then is who, and I believe all three have merits. It's kind of funny that their popularity among Fire Emblem fans is also like...inversely-proportional to how unique they are in Smash lol. Robin is more unique than Chrom, who is more unique than Lucina. In the Fire Emblem fanbase, Lucina is more popular than Chrom, who is more popular than Robin. But Chrom, who would otherwise be the middle of both popularity and uniqueness, is also the only one of the three to have his popularity
as a Smash candidate directly acknowledged on several occasions by Sakurai. I could even see a scenario where he returns without Roy, which is the only echo where I can say that, due to the fact that he still retains like, just as much from Marth as he does Roy.
Roy would then be next, due to his popularity, but offset by him being lower priority in the past. Finally, there's Corrin, who I think is probably the most likely of the eight to be cut.