I think they are called "Comm Nodes" probably because Command suspects them to be. They seemed to be luring the Sathanas fleet into the nebula, since they were clustering in that system in Into the Lion's Den.
I have some points to argue with;
1)Why didn't the Shivans start supernovaing their own stars first before having to invade Ancient, Terran, and Vasudan space? I mean, the stars in the GTVA systems aren't the only ones left, right? (Let's look at it this way. Shivans are, say, billions of lightyears from GTVA space. If they kept turning the stars near to them into nebulas first, then GTVA would have noticed why the universe is running out of stars). The Shivans simply ambushed the Ancients/GTVA for unknown reasons.
2)
if opposition is encountered send in the Lucifer fleet to soften resistance
The Shivans didn't find opposition. They simply shocked the GTA and PVE with their command ship. If so, then either Terrans or Vasudans would've like, killed a number of Shivans, Shivans get mad, and send in a raging Lucifer to obilterate their foes. But no. We see in the FS1 cutscene a pilot screaming like hell about
unknown ships. If they were unknown that means the Terrans and Vasudans never encountered them before, and so they wouldn't be known as enemies to Shivans.
3)
then pull back to their own territory that is still flush with resources leaving the systems opened up by the Knossos portals until it is time to expand again.
Again, there are still billions of stars out there. They should've all been turned to nebulas before the Shivans go system-hopping using Knossoses, trying to find more starts to nebularize.
That.
In mission brief 1 there is suspicious lack of a name for the nebula suggesting that they might not be able to place where they
This actually struck me. There is no name for the nebula. It means that it's like, gigantically far away from GTVA space. If it were near the Terrans/Vasudans should've given it a name ages ago. Knossos Portals are, indeed, used for subspace travel, but I think they're able to transport ships extremely farther than typical trans-system nodes.