Somewhere at Sonic Team is a whole "roadmap of Sonic titles," says head honcho Takashi Iizuka, and the devs "think about which game to release in which year"

Sonic Team head Takashi Iizuka has explained how the studio plans out the releases of Sonic games on a roadmap internally.
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Sonic Racing: CrossWorlds Reveals Yakuza DLC Release Date

CrossWorlds officially confirms the release date for the upcoming Yakuza DLC, with fans able to play as Ichiban Kasuga soon.