Sounds very interesting. The thing with Obi-Wan being the last surviving Jedi helps explain why no one remembers them in the original trilogy, and Maul and Grievous being the villains of the entire trilogy would really help their characters.
Specifically I want Grievous to be the absolute formidable unredeamable monster everyone loves to hate while Maul will be morally grey (like his CW arc which I adore) and conflicted as well as being the Cassandra about Sidious (again like CW). So you get the best of both worlds with villains