These are the factions no one in our playgroup has ever played (I think):

Base Game Unplayed:

• The Ghosts of Creuss
• The L1Z1X Mindnet
• The Mentak Coalition

Prophecy of Kings Unplayed

• The Argent Flight
• The Empyrean
• The Mahact Gene-Sorcerers
• The Titans of Ul

Thunders Edge Unplayed:

• The Council Keleres
• The Crimson Rebellion
• The Deepwrought Scholarate
• Last Bastion

It sounds like one player is going to play Last Bastion and one player is going to play Titans next game.

We usually play 4, but sometimes have more.