That wouldn't make sense in context with Bosch though. The GTVA forms in the context of co-operatione and harmony, in response to the Lucifier and the Shivans. Bosch gets ideas about the Shivans, secedes, starts demanding systems, massacring civilians and sending people to die at GTVA beam cannons. He then starts a full scale rebellion including remnants of the GTVI and builds ETAK. Shivans wander in from Gamma Draconis, annihililate a GTVA cruiser, but when the guy who actually started all the trouble and strife is in their hands, they board his ship, kill all of his crew EXCEPT him and wander off.
They then commit to a full scale assault on the GTVA, wiping out their nebular prescence and stop to blow up the Capella star, after which they either withdraw or vanish.
The Shivans aren't playing nice anymore if they ever were. If they turn up, the only in-character option for them is to begin a full scale assault on both UEF and GTVA territory, probably drawn by whatever experiment the Elders are cooking up. Which may turn out to be the entire reason the GTVA is attacking in the first place. Like I said, I still feel the GTVA hasn't been in character for a great deal of this. If every single person below Admiral was uninformed about their intentions on hitting Earth, you would have had a massive full scale rebellion likely throughout the GTVA without enormous amounts of propaganda before hand. While I like where the story went, just that bit seemed clunky.