It might be consider a cop out but

What if Riot further add to Varus story by adding to Varus the Darkin. We now know Kai and Val story but still little is known about Varus.

What if his story is more like old Varus where he did his duty or follow an order that lead to the near extinction of his race. Add more depth to this hatred he feel against humanity because to him they are the villain that wipe out his kin. Like how old Varus crave vengeance against Noxian, Darkin Varus want it against humanity.