I think you writing, eventually, a prequel showing the age of the biodigital plague would be sweet.
If you haven't thought to do so anyway, it's my suggestion that you do. I'd sure buy it.
I'd like to see a prequel on that as well, though I think it would be best to wait until an appropriate time in the storyline when it really needed. Much like when Ryk added the back-story as to what happened on Earth while Aurora was gone. It seems like story should progress to the point where the main characters learn a fair bit more about what happened before prequel book is added.
I would love a prequel as well. Typically a prequel mid series annoys me but, Ryk could easily do one in between parts. It would be a great break from the usual characters and provide info that could later be used in the next part, like discovered in the data ark. I hope Ryk takes his time in between parts and gets a good vacation, but this would be awesome. Ryk didn't really structure his storyline until several books in, although you I couldn't tell, and this would give us something to hold us over in between parts that I'm sure will be at least 6 months or more between while he plans out the next 15 episodes. A 200k word plus book, maybe even a stand alone, would be awesome!
I was thinking that it would be cool if once the Jung threat has been neutralized (or even while liberating worlds) the alliance tried to gather as much info on the Pre-plague Core. Then over the course of several more expeditions either fighting aliens or time traveling back in time or whatever the Aurora finally gets a clear picture of what happened and in lue of a detailed report we get a flash back to an earlier time. In that vain imagine a two episode segway in part 3-4 could work.
Told from the point of view of investigator who eventually meets with and works with a Junior Senator Scott to find out what happened and whether they find the real reason or not really doesn't matter, in fact leaving an open conclusion to the back story would be frustratingly kinda cool. I mean if they did find a perp or not, it doesn't matter because the need for survival outway the need for justice.