Its not really new but an Idea how the play stile of the Cultists could be used in ES 2 .

Affinity : Bound Together . The Homeworld of the Faction is their so called Coreworld . Every new Colony gets a FIDSI and/or Approvall and/or A population Cap ( something like Max.Cap. : 2) . This Effect ends If the colony is connectet with a Core Worlds System . It connects if its next to a Core World System or if it is next to a Colony that is next to a Core World System and so on . If a Colony is connected it get a small Bonus to FIDSI and/or Aproval and/or Population Cap (something like Max Cap + 3 ) . If the Homeworld is captured the Planet with  the Greatest FIDSI can Become the new  Core World . With advanced Tech it is possible to build More then one Core World ( For Great Costs of course the Boni in the Colony´s doesn´t stack ). The First Core World (or system but i think that would be to strong) gets a better FIDSI and Population Cap Bonus than the Colonys but no Aproval Bonus . Their special Technologies should focus on upgrading their Core Worlds . 

Traits: Slow Fleets , Expensive Colony ships , Better Invading Defenses.

I have different ideas how the backround Story´s could be

Story : 1.The Rebooted are an ancient Robot Mind Hive which was Created by the Virtual Endless to Help them in the War and were a Backup plan . Before the Virtual Endless working on the Project could activate them they got distroyed by Orbital Bombardment . After Thousand of years they got Activated in accident by Dust ,now the Rebooted try to find their places in the Universe ,because the Dust Made a Robbotic Drone Networ to an Hive Mind full of Indeviduals .

2.The Members of the Brotherhood of the Mind were Test subjects to the Concrete endless thousands ago . They got Augmentet with devices to build up a psyonic network . After the Endless left their planet The Brotherhood of the Mind improved the devices so every lifeform of the entire planet is connected in one Giant Mind .

Both Story´s support the Affinity in both cases a Giant Network is needed to connect all the people and the Core Worlds are something like Giant Connectin points.

Please tell me your opinion , Ideas , Thoughts .

And sorry for the bad English .

Yes . You are right . I just had this idea and wanted to throw it in the forum .