Welp, back to speculation.
Things I am 100% sure about:
1. Fighter 5 will be third party.
2. Fighter 5 will be from a series, but not necessarily a company that has never had a playable character in Smash.
3. Fighter 5 is not be represented in the current game whatsoever. No spirits, Assist Trophies, cameos, Mii costumes, or anything.
4. Fighter 5 is not Crash Bandicoot nor Ryu Hayabusa.
Now, with these rules in mind, here are a few characters I believe have the best change due to EVIDENCE:
1. Doom Slayer.
Yes, the leak is dead, but still Bethesda has openly admitted to talking to Nintendo about Smash, and Reggie said before he retired that he does not think the Smash team has EVER been denied a third-party character. Sakurai has also publicly acknowledged John Carmack as the father of FPS's. Doom Slayer also perfectly fits Color Theory and is a gunner, making the playstyles in the Fighter's Pass more diverse than another brawler or swordfighter.
2. Heihachi.
His Mii Costume is suspiciously absent, especially since it was included with Ryu, Akira, and Jackie back in Smash 4, but not with Akira, Jackie, and Terry in Ultimate. He was also confirmed to be considered for Smash 4. Chrom was also considered fir Smash 4 but later brought to Ultimate. Likewise Pac-Man, Miis, and Villager were all considered for Brawl but brought to 4. Point is that Sakurai usually comes around (Chorus Kids confirmed). My biggest doubt though is that I don't think Sakurai would include Heihachi on the same Pass as Terry, let alone directly after.
3. Lloyd Irving
Same boat as Heihachi, but more likely for this pass. The Tales of series icon has also had recent trademarks along with an odd book icon that could easily be the icon used in Smash. Though my personal belief is that we will get a gunner to fit my "variety theory", I could be completely overspeculating, and Lloyd could be our Bboy.
4. Monster Hunter.
Again, missing Mii costumes, plus Rathalos is the only boss in Smash to not have a playable character from his series. Monster Hunter could also satisfy those looking for a female character. Not to mention that Monster Hunter World won some awards at TGA, where the fifth Fighter's Pass character is likely to be revealed.
5. Leon Kennedy / Jill Valentine or Dante
I lump these characters together because they all have the same points in their favor. Sega and Square Enix got new characters in the Fighter's Pass, so why can't Capcom. Both the Resident Evil protagonists and Dante satisfy my "variety theory", being gunners. They would simply be the easiest to obtain. Specifically in Dante's favor, it was said by his creators that Devil May Cry would need a game on Switch before Dante ever joins Smash. That criteria has since been met. Could that have been a hint?
Characters I actively think will NOT be DLC:
1. Sora.
Disney. 'Nuff said.
2. 2B.
To my knowledge, she has not appeared on a Nintendo console even as a cameo, so she's not eligible in my honest opinion.