On a Steam post a Dev seemed to say the 3rd faction could be more different than the current two as the current two come from the same tech tree being both from Earth, while the 3rd won't have those restrictions. That strongly suggests it will be an alien force and not a sub-faction.
I am also very curious about them. I personally hope it is still a high-tech race and not a Zerg type bio-race. I'd prefer something along the lines of the Cybran, with lots of sharp angles on the units. Hopefully a bit more menacing than the existing factions too.
Thank you very much for kind, detailed answer. I greatly appreciate your help. Very intriguing information indeed. Just same as you, I strongly detest, and also quite skeptical, against Zerg- or Tyranid- type bio-race. This game is about Singularity Clarke-tech and physical gods residing in metaverse after all. In addition, I think bio- and ultratech- concept is not intrinsically incompatible, as eminent Grey Goo's Shroud/Silent Ones faction have attested. I personally consider hyper-advanced half-organic, half-machine faction having fancy gorgeous aesthetic would be just as interesting as angular, menacing, cybernetic Cybran-esque, purely mechanical alien faction having minimalistic, utilitarian aesthetic.