So there's a glitch suggesting that they might be working on a duo character?
Mighty and Ray from Sonic Mania (please be Mighty and Ray and not Classic Sonic and Tails please please please, no more Classic Sonic for a while)
Cream the Rabbit with Cheese the Chao (great left field pick. Throw in a Chao Garden stage to soften the rage)
Commenting the Sonic picks because why not:
I would be happy with Sonic & Tails as a duo character, honestly... classic or modern doesn't make much difference for me, though since modern is already in the game maybe the duo being in with their classic design would be the only possible option; they had a decent amount of tag moves in several games, and while Super Sonic is the perfect final smash for Sonic, it would be cool if Sonic & Tails would jump aboard the Tornado and shoot the opponents on the stage.
Mighty & Ray are... fine I guess... but I'd rather them be Sonic and Tails, Mighty and Ray are still too little developed as characters and too much obscure despite being in Mania.
Cream the Rabbit, I like the character but I doubt she would fit a fighting game (I know, Sonic Battle, but still). She's not really a fighter at all (even canon-wise, she hates violence); I know that there are non-fighters in the game already, but in Cream's case, most of her attacks would be about launching Cheese at the opponents, I doubt you could make a creative moveset out of just that (she's definitely more suited for platforming than fighting). Unless they make her the equivalent of Animal Crossing's "Villager" to Chao Garden and make her fight using Chao Garden elements, like planting seeds and making trees grow under the opponents (like Villager) or uhmm throw fruits? Cheese plays the toy trumpet VERY loud? A beach ball as a bullet? I don't know, but now that I think, that minigame from the Tiny Chao Garden of Sonic Advance 2 would be a cute
up-special (I mean down special, since it doesn't recover);
but doubt they would even consider Cream when Tails, Knuckles, Eggman and others are still not in the game.
As for the stage, Chao Gardens are cool and all, but Music Plant or riot (the only other accettable option is Ice Paradise).
But assuming that the next fighter is a duo for real, does it mean that Adeleine & Ribbon have a chance again? I really doubt it but if it turns out to be the case, I'm obligated to get game+dlc regardless of my opinion on it, even just to say thank you.