So hot take but I don’t think Sonic is getting another character, not even an Echo Fighter.
Not only has the popularity of the series severely dwindled down thanks to things like Forces and the movie, but Sonic also isn’t and never really was very popular in Japan, as a person who just went there I can say that he’s mostly used as a corporate mascot used to advertise SEGA products rather than his own games, and hardly any merchandise of him actually is sold there.
Honestly I’m at the point where I think a second Persona character and characters like Arle and Kiryu are more likely than a second Sonic rep, as Persona, Puyo Puyo, and Yakuza seem to be the current big three of SEGA. (I could also see Jeanne as a Bayo Echo If Bayo 3 ever comes out)