The 0th Unit is still around in X7? I don't have X7 or a book for it, but my book for X6 lists X as former captain of the 17th Unit already. And the timeline in the Compendium gives the reorganization coming between X5 and X6, for what it's worth.
Signas does remind me of Colonel in some respects, and I like both characters. But I think you may be giving him too much credit here. I know he's supposed to have the best processor and the best judgment, but what does he really do? In the storyline when he appears, do the Hunters really have better information or make better decisions?
Using the 'vision' of the Virus is a fascinating concept, and I could see someone trying to build it. But if they ever had a success, I'd expect it to be a more amazing character (sorry, Signas).