I'd had my tool taken out, just realized.
It seems to me that in G5 the Serviles aren't at all happy with the Drakons and the Humans are getting annoyed also, not to forget the Drayks. A Servile faction wouldnt be that hard to fit into the story, Lets say Penta/Kaz/any old sevile (with supporters) are getting annoyed at the Drakons for being arrogant and treating them like inferiors. He gets you kill a Drakon general, maybe Akhari Blaze, and then you could go to the Council and get them to sign a treaty so they could like side by side or half island each or something. Then end game is you kill Ghraldring etc same as other factions.
Or alternatively you could go for all out domination, you kill the council for Ghraldring, then later double cross him and kill him, although thinking about the Shapers sounds easier to kill than the Drakons, so maybe the other way around. Then they either stay on Terrestia or they hop of to Sucia Island to retire.