Nakamura has a fine track record outside 06. He was the director of Sonic 06 but he was also responsible for directing Samba de Amigo, Billy Hatcher and Rhythm Thief.
About the third style, going by the pattern of Classic and Modern, it will likely be Adventure Sonic or Boom Sonic. Only reasoning I am skeptical about Boom Sonic otherwise is that the continuty is not quite like the dynamic Classic and Modern Sonic has. Also I'm waiting for the panic button if Boom shows up. But under a different dev team probably be a surprising good gameplay style.
A chao garden would wrap up the game's content well. Having Tails or Knuckles playable be nice.
Another possibility is Eggman playable. "Forces" reminds me of factions and would be interesting to play as Eggman again.