If you connect the dots, you can see how Grevious was originally planned. The stories and artwork in Visionaries were created by writers, storyboard artists, etc. that had worked on Episode 3. Look at Grevious's early artwork and design images... the eyes behind that mask are Mauls.. its unmistakable in my opinion. I think that Grevious was going to be one of the big reveals in Sith. Image Obi and Grevious in a long drawn out Saber fight on Utapuu as clones flood the place. The video game version of the Obi-Wan Grevious fight was so much better than the movie.. would have been perfect. Obi damages Grevious' mask and the front panel falls away to reveal Maul's black face. Follow that up with a little speech similar to the "I fell a long way that day" speech from the comic.. and end in a similar way to Sith Grevious demise. Obi-Wan hanging there would have added an extra depth to the scene with Grevious being Maul.
However, everyone started to talk about Maul being Grevious after the production pictures started to leak. I really think Lucas decided to change it at the last minute to avoid that. And, I think Grevious suffered for that. The only respect I have for Grevious as a villian comes from the Clone Wars cartoon. If you just take him for what we saw in ROTS, he's no more than a pimped-out battle droid. That's why I could never get into the PF... character was just too weak to be worth the money.