In a similar vein to the recent elevation of the Hisso, the Pilgrims could be a viable faction with unique playstyles.  For example, a hybrid between United Empire, Vaulters and  Vodayni: replantable colonies, and entire system can be abandoned to allow instant colonization of a new planetary system (assuming habitable planets), along with population ships (similar to Arks) or Orbital Habitats to increase the number of pop slots while perhaps accruing a reduced production capactity for the extra pops.