Lots have been mentioned in countless threads before, like more Jedi/Clone synergies, synergy between luke/Leia, Changing chewy to rebel for chewy/Han, Maul/savage (like you suggested) EP/Vader, EP/RG, GK/JKA, JKA/Ahsoka (more then it is) Boba/Dengar, GG/IG-100 Magnaguard, Dooku/Sidious, Dooku/Ventress, Lando/Lobot, Old Ben/Luke, Vader/Stormtroopers, Revan when he drops and HK-47, etc
I think over time they'll add synergy to the majority of toons to keep the game fresh as well as change seeing all the same squads at the top. Right meow we are mainly at two toon synergy, but over time I expect 5 toon synergy, especially the squads that can have 5 toons that are known to be together in the movies/tv shows I.E. EP/Vader/RG/Stormtrooper/Tarkin, Old Ben/Luke/Leia/Chewy/Han, Yoda/Mace/GK/JKA/Ahsoka, One of the Jedi generals/4 clones, Dooku/GG/B2/Gunray/IG-100 Magnaguard, etc