I’d love to be able to join the Swarm (Choose Your Own), and there are the other factions at Venice (e.g. Druids) we haven’t seen anything of. But to pop culture, that mostly leads in the direction of major IPs.
While it wouldn’t blend with the game style, I can’t help but want a group of bees who reject the factions and instead try to be superheros in a disorganised but well-meaning kind of way while on-the-run from the big secret societies. Like a cross between Ghostbusters, the Defenders and Orphan Black.
They probably won’t add a new faction, as they’re downplaying the current ones, but some ideas of new factions could always be taken forward as a cross-faction reputation style system. We cross paths with an NPC fighting the same dude we are we join their club via a few trials and help out occasionally. We have this kind of relationship with some NPCs who randomly phone us with a problem for us to sort out, but it would be a formal kind of thing.