Today, during the Sonic Panel at Austin's SXSW Gaming event Sonic Team revealed that Project Sonic 2017 will officially be called Sonic Forces.
This comes from the fact that the game will explore the "Forces of Good and Evil" - it's possible we could see something similar to Sonic Adventure 2 and its different storylines.
It was also revealed that Sonic Forces would be running on the "Hedgehog Engine 2" with the first Hedgehog Engine being the one used for Sonic Generations. The wisp mechanic from Sonic Colors will also be used in the game, while the level-design will be non-linear like Generations, in which there were multiple paths through the levels.
Sonic Forces is planned for release on Switch sometime this year, and the team confirmed that we'll hear more specific details come E3 2017.