Ok, let's be honest here, we know virtually nothing about this and we can't possibly guess with any real degree of accuracy, it's just going to be kept hidden until the day they release it, if it ever comes. Personally I like the idea of it remaining an eternal mystery but I still want to know!
But, this aside, I'll throw in my opinion.
Right, so the only things we know are:
• It's stupid enough (or insentient enough) to keep taking out the warning beacons they drop; any intelligent enemy would leave them for surprise/stealth value
• It's completely unconventional, not a simple rebellion or anything of the sort or else it just wouldn't be what it is, i.e., capable of driving a crew mad and completely unstoppable. It has to be something just simply... other.
• The Vasari are somehow responsible for it, a 'terror of their own making'. So if we take this literally probably phase or nanite related, those being their specialities.
By this reasoning, I've seen three plausible answers (not counting the Interstellar Revenue Service which is simply genius...)
1. A massive nanite cloud; an incomprehensibly big, yet virtually invisible swarm, devouring and converting everything in its path. To me this seems the most likely and accounts for virtually everything. It could be an experiment gone wrong, it would take out the beacons, could easily destroy even the dark armada and would potentially drive a crew mad with fear. However, it's also the most literal one and I can't help but feel I'd be disappointed if it was the answer.
2. Some sort of 'phasic wave'. A huge pulse, like a supernova but more powerful and with a much longer range.
Simple and effective but leaves too much unanswered, mainly speed and power (why would one ship survive and why wouldn't it have caught up with them) but with a few tweaks could make sense.
3. The most flimsy but possibly the most likely : some sort of phase space-dwelling race. An alternate dimension type who were accidentally unleashed by the Vasari, with no real concept of our universe (being so totally different in nature and origin) they only seek to destroy.
As I said flimsy, but I think it's got potential.
Of course, as I said, the actual answer is probably so off the wall we couldn't possibly guess it, there's no reason for them to give us any solid hints whatsoever. In reality I really think the good money is on that they haven't even thought about it properly yet, just throwing in a bit of mystery to spice up the backstory. But hey, hasn't stopped us from guessing so far.
Thoughts anyone?
Oh, and P.S., no care-bears. I know, I saw, I laughed. That's it.
