It's four in the morning, I have to "wake up" for work in about an hour, so I'll make this concise.
I think if you're going to get anywhere with Shivan theories (aside from going straight to the source), your best bet is to think small.
It's more or less established that Shivans are a hive-mind culture, and yet I haven't seen anyone mention ants or bees or similar hive-based insects yet. Exoskeletal, ridiculous size/strength ratio, heck, even compound vision (seven "eyes"?)...
Let's have a look at some
context. (I apologize for using Wikipedia - as I said, it's VERY late.)
I don't think it's correct to assume Shivans are a tool, simply because of their technological enhancements. Rather, consider them
an introduced species. "Symptom of a larger problem," reads the quote? Context again: red fire ants are only
one introduced species. What if the larger problem isn't any kind of galactic war or sleeper race, but pest control?
More interesting, could the Shivans be viewing US as the introduced species? (Terrans, Vasudans both?). Disturbances in the environment, in this case, Subspace. Not to label them environmental protectors, but perhaps a weird hybrid of territorial mindset and exterminator philosophy.
Yes, that one goes back to what was said earlier about stepping on their subspace turf, but perhaps for different reasons.
FS1 - Lucifer
et al, perhaps a relocating "queen" Shivan looking to nest, and finding itself in hostile territory?
FS2 - The ants come boiling up out of the nebula to chew your feet off. Blowing up Capella... making more territory? More nebula and star material - maybe nebulas are as close to a 'natural' environment as a Shivan can get.
I'm rambling, so I'll stop now, but I'm curious to see if anyone else has thought in this sort of direction before, and where it ended up.