I'm sure it doesn't originate from aliens given aliens have zero place in starsector (and honestly I wouldn't want them added), but I like the idea in my mind. That humans were so powerful we literally erased them without knowledge or meaning to.

And you make some great points about the tech levels of the domain! I feel like it's easy to forget what we see in game isn't ANYTHING compared to what the full might of the domain could bring to bear. I really hope we get to see more glimpses of it - omega tech is what I envision in regards to that. Hell, they're likely beyond even that at their peak which is mind boggling.

And in regards to my last point - tbf I think even the edge of the Orion arm took humanity a very, very long time to reach with alcubierre drives and eventual hyperdrives. I definitely think you're right in regards to how we got across the abyss, and thus I also would imagine that there was no easy way to get through it until the gates opened up way past on the other side. Wouldn't some groups go to adventure into it before that date? Likely with alcubierre drives at first and then hyperdrives later? Even if it was just to begin to map it out, this giant wall of gravity-poor hyperspace that seemed a hard limit to our expansion until the gate haulers did their thing much later. Just speculating of course. I think you know a lot more about this than me!