Well since I'm mostly restricting myself to worldbuilding around overtly ambitious project that likely never materialize I can think out what I want.

In my FS1 that would be
-a more smooth representation of the Vasudans, primarily as a danger (ST of all things did a better job at that)
-also an adpation of tactics compared to the TV-War
-a retcon that the Shivans use full FS2 armament (beams and everything)

So the Great War would be short but immensly destructive. Since there'd also be TV-War prolog, you could see how these pre-beam Orions, that just seemed so powerful, would get threatend by a trio of Cains; so you could feel like Lt.Ash fighting invulnerable, deadly ships despite sitting on 14 years of subspace war experience.