Here some factions that I found in the XMLs that are, or will appear eventually probably as minor factions later in game. The list is incomplete, some names are placeholders and some were deleted.

Steam/SteamApps/Common/Endless Space 2/Public/Plugins/GalaxyGenerator/GalaxySettings.XML

<Trait Name="AffinityTerran"> UE?

<Trait Name="AffinitySwarm">  Cravers?

<Trait Name="AffinityAmoeba">

<Trait Name="AffinitySophon">

<Trait Name="AffinityResistance">  Pilgrims?

<Trait Name="AffinityHoratio">

<Trait Name="AffinitySower">

<Trait Name="AffinityHissho">

<Trait Name="AffinityAutomaton">

<Trait Name="AffinityEmperor">  TimeLords?

<Trait Name="AffinityHarmony">

<Trait Name="AffinityVaulter">