To be honest, I’m very confident that the last fighter is going to be a Sonic representative, I just have this gut feeling for a few reasons:
-There hasn’t been any brand new companies represented in Fighters Pass vol 2, the only ones left are Capcom and Sega, I doubt a Capcom rep will be the last, though this could change but it’s hard to say for sure.
-The entirety of Fighters Pass vol 2 thus far seems to be filling missing gaps of Smash Ultimate instead of expanding to new areas like with Fighters Pass 1
-Sega hasn't received any new content for Fighters Pass vol 2 (unless if you count the Sophia spirit, which even then, is Altus), No brand new Sega Mii costumes have been added since Joker’s Mii wave
-For a Sega rep, it would make huge sense to have it be Sonic on Nintendo’s end, It’s one of Sega’s biggest, money-making franchises and it’d be hard for me to imagine it not being Sonic.
-This one is likely stretching it, but during the Sonic Central back in May, the presenter stated to “look forward to more crossovers throughout the year”, correct me if I’m wrong, but we’ve basically received no new crossovers since the ones that were already announced in that presentation, it’d be the perfect opportunity for them to announce another Sonic rep in Smash.
I think it’s very likely but that’s just me.
I want to touch on this point specifically
I wanted to make a entire post about this, but I'll do it here. If the whole thing about Fighter Pass 2 is not just adding in New characters, but filling holes in the Roster, than another Sonic character is a missing key to that
Ultimately, The fact that Sakurai and the Team did add in characters like Ken Masters, and Sephiroth into the roster despite their Franchises (and even Specific games) being represented already showcase the importance in terms of representing Guest Franchises a certain way
Adding Ryu and Cloud especially could be considered Miracles in terms of having them in Smash, but with that being said, that doesn't mean the Representation is Ideal, or up to par. This was especially true with Cloud
Ken and Sephiroth help make the representation of these Franchises more alive and up to par in the same way that adding characters like Bowser and Peach in Melee for Mario, Zelda and Ganondorf in Melee for Zelda, Meta Knight and King Dedede in Brawl for Kirby, and even Newcomers like Ridley and K.Rool for their franchises did. Ultimately a Gaming Franchise is not just elevated by the Main and/or Title character, but also the supporting Cast
This is especially True for Sonic. Sonic has among the Most Iconic and Popular cast of characters in Gaming history besides just Sonic Himself. This is not only true outside of Smash, but also inside of Smash, as Characters like Tails, Shadow & Knuckles, and now more recent Eggman have been very requested characters to be added in, especially in the Casual Circles of Smash Speculation
So Sonic still only having 1 character is a Missing gap, not just because of the fact that a Franchise as Big and well known as Sonic (who's been in more Smash games than not been in one), but more importantly, because the Supporting Characters themselves are Popular, Iconic, and have had many requests to join the roster, and are very well acquainted with the Nintendo audience
There's also another Aspect of this that really only Shadow specifically could kind of fix. Sonic himself has had alot of his Complaints about his moveset feeling dry and not having enough flair that he should have, and that even other 3rd party characters have. Ultimately I think the main problem (besides the nerfed amount of expression that's most likely thanks to Sega, not Sakurai) is that Sonic doesn't have alot of the Modern Flair that made him even more cool than already before, Since Sonic is more based of the Classic days, instead of the more modern Era. That's why alot of his Attacks come from Sonic the Fighters and the Genesis days, with not much from Sonic Battle and from Adventure onwards
Sakurai is someone that doesn't like to Radically change movesets, so it's likely Sonic is gonna stay the same way as of now...However Shadow, while his own character, is meant to be a reflection of Sonic, and this includes having Similar Abilities. in the same way that Kids wanted a Sonic game where he can use guns, people want a Sonic that has some of the more modern Flair that they are looking for, and while Sonic himself might not be changed to fit that criteria, Shadow is the perfect Standin
Not only can he use some of the Cool Modern techniques Sonic doesn't use like Light Speed Dash, Boost, Black Tornado, etc, but Shadow also has access to his own flair in his Chaos Abilities, as well as having a more combat, more lethal form of Combat compared to Sonic.