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.
Polygon

Sonic the Hedgehog is so back, but for real this time

Look, I know that what I’m about to say is going to bring out the skeptics. It’s a claim that a certain subset of gamers have been repeating in some form for God knows how many years, trying to play ...