I agree with folk who think this must be plot, and probably end game, related. I just can’t see why something that wasn’t intended as a plot twist or surprise story reveal would need to be kept secret for years, and why players would only find out about it after the release, if that part of the quote mentioned by the OP is an accurate representation of what Swen said.
As to what it might be, there seem to be so many possibilities. It does seem reasonable that it’s something tied to earlier games and/or the wider FR setting given apparently folk were talking about it from the start. Possibly something to do with why we’re suddenly seeing a nautiloid when apparently they were meant to be long gone or at least vanishingly rare?
"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"
