OK, the dev's said there will be a clues in Rebellion as to what is chasing the Vasari and apparently it's not Sam Neil returning in a ship that vanished into a black hole for fifty years.
They also suggested that they thought it was possible some might get it rather quickly.
To this end, I posit my guess.
I kept noticing in the varying screen shots the new Vasari ships. We know the Vasari are quite happy to have institutionalized slavery and to force it on advanced but less powerful empires.
There's one theme in all the ships I saw..."Bugs Mr. Rico...zillions of 'em!".
I suggest the Vasari "assimilated" a space-faring insect species and experimented on them to gain their weapons and travel capabilities.
Ever poke a stick into a wasp hive? I did once. There was a wee hole in the ground about three inches deep with a single yellow jacket in the bottom of it. I killed it with a stick and then discovered that it was the entrance to a hive.
Ever see the cartoons where the moving swarm comes out after the cartoon character? That's what happened. A massive "nanite" cloud of angry wasps came out and chased my brother and I to the back door of my grandmother's house. She wouldn't open it because they were bouncing off the screen like machine gun bullets. We ran to the front door on the other side of the house and when she got there, she couldn't open it either as they had followed us around.
Finally my aunt let us in and threw wet blankets over us and brushed us off with brooms. I had been stung 32 times and had wasps in my nostrils, the corner of my eyes, between all of my fingers and dozens embedded by stingers in my belt, shoes and jeans. The city sent an extermination crew out the next day and after gassing the hive dug it open. It was 4 feet deep, 15 feet wide and 32 feet long.
I believe the Vasari poked a stick into a hive and now the swarm is after them.
If I am vetted officially at some point as being correct, I prefer to be thereafter referred to by name with the honorific, "Most Mighty and Wise" prefacing it.
Thank you.