David Braben replied recently ( I believe it was the Horizon's launch livestream) to a question about whether we'll ever get access to other galaxies, he said no. Our own galaxy in game is already supremely massive, with whole sectors locked off for future content.
So it's probably safe to assume that the barnacles have nothing to do with the Magellanic Clouds.
We can't go to them, but it doesn't mean "they" can't come to us
Could be we are just getting drives that allow far bigger jumps.