Along those lines (since it matches something I've been pondering). It seems reasonable to me to assume the UAs were heading *away* from Merope. I've recently wondered if it's a life cycle kind of thing, they hit some system with the right sun, and then become UPs and return to Merope.
The UA's were heading away, the UPs are heading back. The Fed's figured it out and are scooping them up at the source. At some level that implies the ones heading back found what they were looking for before reaching the 135-150LY shell so what if any unique stars are in that bubble ?
I've also pondered whether you can't find UPs, you have to drop a UA where they can evolve. So I have a few that I'm hoping will 'evolve'.
Speaking evolving a UA makes me think of pokemon... silly pokemon Go.... Back to seriousness. That is quite possible, I just haven't seen any game mechanics that allow a transformation. Most of what we have found is from game mechanics despite some of our wilder ideas, not to say we shouldnt think outside the box and try crazy things. At the end of the day we should keep Occam's razor in mind.
For your theory I'd also consider if something in the cargo hold may trigger that change....