I would say that if it can be done well, then Grievous should be Maul. However, if it can't be done really well, then I would be fine with that. In it's own way, it could recall the serial feel with the different villains, and it also works within the context of it being a war, and having different heroes and enemies, etc. But, I don't want to make Grievous be Maul, and then have it done in a way that's kind of half-baked. It should really work, or we should just make the best we can of Grievous through dubbing or what-have-you.