Jim Carrey's Dr Robotnik is unarguably a major draw to the Sonic film series. There is no way the next film is cancelled or rebooted, but if he truly intends to retire the writers are going to need a new proper threat. A movie all about Agent Stone and Shadow just would not work.
One of the more consistent concepts I have seen around is of people suggesting a recast in the context of Robot Robotnik from the Archie Comics. I do not know too terribly much about the lore there other than he was canonically dead before and they needed a way to use the Sonic Adventure era design for him. It also gave them a decent reason to rename him Eggman.
I think a decent option would be to just have Gerald Robotnik written as Ivo's father and have someone like Christopher Walken just make him effectively an original character. Maybe the Knuckles Paramount+ series could introduce another villain too.
One of the more consistent concepts I have seen around is of people suggesting a recast in the context of Robot Robotnik from the Archie Comics. I do not know too terribly much about the lore there other than he was canonically dead before and they needed a way to use the Sonic Adventure era design for him. It also gave them a decent reason to rename him Eggman.
I think a decent option would be to just have Gerald Robotnik written as Ivo's father and have someone like Christopher Walken just make him effectively an original character. Maybe the Knuckles Paramount+ series could introduce another villain too.