The issue with "homeworld" is - what do you mean exactly?
It's possible (maybe probable) that the Thargoids are extra-galactic in some way. It's always been a theory that's been floating around in old lore, new lore and lots of speculation on these forums.
If that's the case then the Thargoids homeworld (as in, planet where they evolved) isn't in our Galaxy at all.
However, as you've said, we do know there's "something" in the Col70 sector, although it might just be a beachhead in our galaxy. There's an idea that the maps shown in the Thargoid ground sites are the Thargoids home galaxy (or home reality, or witchspace), the blobs might be territory they've conquered. It's equally possible that it's the 45th Galaxy they've fully conquered in a billion-year expansion across the cosmos - we might just be seeing the very first edge of the expansion wave reaching our galaxy. Again, in a situation like this, the Thargoid Homeworld might not even exist any more!
If the analogy between Thargoids and Ants is correct then each time they start a new colony, then it's essentially like starting a new race entirely (each Any colony is entirely separate fro the one that spawned it). Which means wherever the new queen is located is the "homeworld" - for example, it's possible that since the Pleiades shell is centred on Merope 5C, that's where the Queen is located (or will be located). It's possible that the system in the Col70 sector is a similar "homeworld" for the queen in that area. There's not really any way of knowing just yet, but there's also no way to know what "Thargoid Homeworld" means.
That's not that far fetched, for example Earth is our "homeworld", but it's a polluted mess and it's not really that important any more - so if the Thargoids went to Sol right now and carpet bombed the Earth, other than it being annoying for historians, it wouldn't really affect anything. Even if they took out the entire Sol system (and Mars as the seat of Federal Government), then we've still got the Alliance and the Empire (and arguably Colonia) left as independent functioning governments, let alone the independent unaligned groups - so, where's our Homeworld? I'm not even sure any humans are born on Earth any more, so where is the homeworld of humanity if any alien were to come looking for it? Achernar? Alioth? Mars? Colonia?
There's also theories that the Thargoids are the product of Guardian genetic tinkering, or that they are the Guardians in some far-evolved form, or that they are the Guardian AI evolved over a million years into a more bio-mechanical form. If any of these are the case, there's an argument to be made that the Thargoids don't have a homeworld, as such.
I guess my point is - while it would be interesting to locate the origin point of the Thargoids - I'm not sure finding a "homeworld" would be useful in any practical way. Right now it seems we're lacking in virtually any information whatsoever
I do think you're right though, I think there's some mystery left in the Link spectrograph, there's a few bits that have never been fully understood, but they don't seem to be relevant to anything in particular. I expect it'll be one of those things where next year we'll look at them again and say "ahh, look, that bit means this, makes sense now!" or something
. So in respect of this, it is entirely possible to take goid tech into goid populated space. It is also possible to outrun a goid ship and avoid being scanned by boostin from the goid cloud until the objects inside the cloud disappear. The goid will follow until then and then open a worm hole.
propaganda?