Having watched 3 episodes of Lego Star Wars: the Freemakers Adventures, getting past the zany hijinks and how they're all made of Lego, the show makes a great case for a fourth faction.
Call the Freemaker siblings, Citizens of the Galaxy or Merchants and Commonfolk. Whatever, it is, the main characters are not on any side of the Galactic Civil War (at least not in the first few episodes). They are at odds with Scum and Villainy and have entanglements with both Imperials and Rebels
It's a new spin on the Star Wars galaxy. One that's not directly part of the Skywalker soap opera or the Rebellion. Just everyday people in a galaxy far, far away trying to make ends meet.
While it would be great to see non-Lego versions of the ships and characters from Freemaker Adventures, the Citizens of the Galaxy Fourth Faction doesn't even need to pull from this source.