I highly disagree with Grievous having Magnaguard synergy because of the following 2 points:
1. I spent over 7 months to get Grievous to 7* and I dislike the Idea to farm another character just for him to be viable or something like that.
2. It's like saying that the Royal Guard should have synergies with Emperor Palpatine. While both Royal- and Magnaguards were designed to protect Grievous/Palpatine, they are not dependent on them.
As far as I know, there are datamines for Nute Gunray and his Trade Federation battleship as fleet commander, the Vulture Droid, Hyena Bomber, Droid Trifighter and the ship of the Magnaguard which I forgot the name of.
We also have already B1-Battledroids and Commando droids as enemy NPCs in the light side battles and they just need to be made into actual characters. Droidekas are still missing tho
Edit: Also we need a big Grievous rework.