I've been watching Clone Wars lately and was just thinking it'd be cool to add some more characters from this series. Some of my thoughts were:
King Katuunko and a Toydarian Royal Guard to add to the Republic faction. King could be a support like many dark side characters (Tarkin, Veers, Nute) and the Royal Guard a tank, with synergies between them.
Some more unique clones, such as Lieutenant Thire, Jek, Rys and Marshal Commander Wolffe to add variety and mix up the clone squad. Could also have a clone in the pilot gear with an accompanying V-19 or Y-wing starfighter.
And of course, Padme is probably the most important character from the series not in the game yet. I could see her as a hybrid melee/ranged, like Sabine, but as a support rather than attacker.
Speaking of ships, the Magnaguard had fighters as well, and they could do another multi-person ship with Anakin, General Kenobi and R2 in the Twilight.
I think they've been doing a good job adding characters from the current Star Wars media (Rebels and Rogue One) but they could definitely flesh out some more from older content.