Sonic Armageddon

Sonic Armageddon was a planned film by Ben Hurst (writer of Sonic: The Animated Series and Sonic Underground) alongside Ken Penders, the writer of Sonic Archie comics) Based on the Saturday morning cartoon Sonic: The Animated Series, and proposed to Sega.

Plot
From the looks of the storyboards, it looks like the film would be about Mobius exploiting, so it would likely serve as a sequel to the Sonic the Hedgehog animated series.

Why It Was Cancelled

 * 1) Sega was already busy with Sonic X.

Result

 * The film was permanently cancelled.
 * Sony Pictures took over the rights to make a film, but was later sold to Paramount Pictures which released the film on February 14, 2020.