With classic Sonic being retconed from time travel to an alternate dimension it's looking like Sega are treating classic and modern as seperate brands with each side having a shared core cast and other characters being kept for one side of the franchise.
Both get access to Sonic, Tails, Knuckles, Amy, Eggman and Metal Sonic.
Modern has everyone else introduced or updated from Adventure onwards.
Classic gets to use the previously abandoned characters like Fang, Mighty and Ray.