What Could Have Been: The show's third season was completely laid out and prepared, and then ABC cancelled it.
Knuckles would have appeared in the third season.
According to the series bible, Nate Morgan from the Archie comics was originally supposed to appear in the show. Also, Snivley's original name was Quizley, and he was Robotnik's second cousin twice removed on his mother's side rather than his nephew.
What Could Have Been: This was one of many attempts at making a SatAM game revolving around stealth rather than speed. The closest these elements ever got to being included in a finished Sonic game was Sonic 3D Blast, which excised all of the SATAM elements and ended up being a Flickyrevival, and Sonic Spinball, which relegates the SATAM cast to cameos in a minigame.