Everyone has their own opinion on what is chasing them, from a swarm of nanobots the Vasari made that got out of control to care bears.
The Advent Rebels think that something has corrupted the Unity. The Advent only attacked the TEC after the arrival of the Vasari. Perhaps the force pursuing the Vasari corrupted the Advent? Their level of Psychic attunement may have made them more sensitive to this force.
I also think that the evil the Advent Rebels found in the unity is related to what is chasing the Vasari. However I think its because whatever they are, are also telepathic, and where able infiltrate the unity without the loyalists knowing and the Rebels being able to figure out what it was. This doesn't necessarily conflict with the OP's idea though, perhaps the Vasari accidentally connected to another dimension that let these guys in.
Sorry if the pic makes me look like a noob-hating curmudgeon,
Alright, seriously, enough with the ponies. If you want to put a thread for you guys that's totally fine, but it gets old seeing them in every single new thread that comes up. Unless it has a space helmet on, you can post space ponies at any time.
but I've seen this issue dredged up so many times since the Rebellion Beta came out. The modders would be the most likely to find it since they work on an intimate level with the game's workings, and that is the level that the clues are supposedly on. They found nothing. The guy who said that "the clues are in the game code" either was hyping or just hid the clues REALLY well, as I've heard no actual confirmation of clues.
The guy actually said he knew us modders would be looking in the game files for it, and deliberately didn't put it in there. I believe whatever he put in is hidden directly in the .exe somewhere, which we can't access, or perhaps hidden in a texture file somewhere. My bet is that doing some weird combination of things will unlock basically a hidden achievement that will give the hint, because that actually has to be done in game, but who knows.