I think this theory is brilliant, based on evidence, and should definitely be considered.
It would mean we are not searching for their home world in the first place. Possibly, there is no home world anymore at all. If I understand Nutter right, these motherships are remnants from the first Thargoid war where humanity didn't face their main force. That one was hit by the Mycoid virus and spiralled into the ground where it stayed until now. The scavengers are currently repairing the wrecked motherships with Meta-Alloys until they're ready to rise again. That would explain the barnacle "refuels", for example. It furthermore would explain the "green goo" corrosion visible on the hull and the Scavenger's behavior, in fact, their very presence at the sites at all. Meanwhile, Thargons bringing MAs from the barnacles to the crash sites for repair and so on. It would also explain why the wrecks seem to be so old and why all of them seem to have crashed at roughly the same time.
Leaves the question how they plan to lift up again, as I see it, they're buried flat on their face. Luckily, the main force was stopped in the Pleiades, so the bubble is safe. For now
Yo, O7,
[noob]
TBH, I would say its a plausible hypothesis. There are many possible explanation to what we know and observe, and this is just one of them.
EVEN if it came to be true, still doesn't explain the biggest mistery of all: Why do the Thargoids use morse code?
Before anyone says "dude, this is a game", remember that David Braben wanted to make the aliens "truly aliens". If he keeps his word, there must be an explanation on why they use this human language.