I would say the existence of Sauria does allude to Krystal's existence since it implies Tricky and other characters from that planet exist as well.
And as far as your other points go that can be said about any reboot. We could be here all day listing all of the reasons why we think Krystal could or could not appear in the next Star Fox game. Interestingly enough the most hate she ever received was from Star Fox 64 fanboys who claimed her addtion to the series made it bad and was leading to poor sales of the games she was in. After SFZ bombed I think her chances of coming back are very high.
EDIT: I misread a bit of your post and have edited mine accordingly now that I went back and reread yours. My bad.
The most recent Star Fox bombed. = Krystal now has a high chance of returning.
I don't think that's how that works.
Also, the existence of Sauria doesn't imply the existence of Krystal or Tricky because we don't see any other information regarding the planet. Since Zero is a reboot there's no guarantee they'd return even if Sauria does. It is a possibility that the return of Sauria
may hint that elements from Adventures such as the return of Krystal
could potentially happen but there's no concrete info. And I don't at all get the logic behind saying she has a very high chance because the most recent game in the series is performed poorly.
As you said, we can go back and forth about whether she may or may not return, but that's exactly my point as well. Zero's failure doesn't necessarily mean they'll return to where they left off with Command in the previous timeline or suddenly decide to add her in the new one.
That aside, I can agree that the hate for Krystal was unwarranted, but it's pretty much a guilt by association thing. Adventures was haphazardly turned into a Star Fox game, despite being nothing like a Star fox, so of course people awaiting the next game were either confused or upset (or both.) They didn't like Adventures, and by extension, didn't like Krystal.
I can understand a lot of the complaints regarding Command though. Story and the portrayal of most of the cast was pretty off, with Krystal getting hit especially hard by the poor direction.
Adventures was received poorly because people many didn't see it as a Star Fox game, not because of Krystal. Command was just kind of bad in certain aspects.
And of course many just don't like Krystal as a character which is understandable.
All that I know is that typically, every fighter from the same series uses the exact same victory theme, with a few of them getting alternate remixes, which was the case with Meta Knight, Bowser, and Bowser Jr.. Rosalina and Dark Pit were the only odd ones of the bunch, as their victory themes did not match what their series symbols normally use.
Now, it would've been less of an issue if Rosalina had a Grand Star symbol, while Dark Pit had a mirrored version of the Kid Icarus series symbol. However, Rosalina was only a supporting character in the two Super Mario Galaxy titles, while Dark Pit's role in Kid Icarus Uprising was just playing the anti-hero role (much like how Shadow was the anti-hero when he made his debut in Sonic Adventure 2).
I think that would've been more of an issue actually. My point wasn't inconsistency among whether they had a unique symbol to match a unique fanfare jingle (that seems like even more of an arbitrary change tbh). I was arguing in favor of keeping the fanfare consistent among all characters of the same series. Giving some characters unique emblems would make things even more inconsistent imo.
The series emblem and fanfare are meant to be representative of the series that a character hails from, which is why I'm more in favor of keeping both those things consistent. If each character had music that followed the fanfare to play over the results screen in a similar fashion to Cloud, then that I'd be in favor of.
And I'm well aware that Cloud's fanfare, the FFVII victory theme, is a single piece of music, but my point is that the it retains the first few notes used throughout fanfare in the entirety of the Final Fantasy series. My suggestion is to do something similar in Smash by retaining the series fanfare, which would then trail off into a track unique to each character.
This keeps the series traits consistent while giving each character something of their own as many have wanted.