The Borealis will be a location in the game, but GLaDOS appearing is somewhat unlikely (unless the theory that she is the Overwatch Dispatch is correct).
Maybe we might actually met some aperture personal. YAY!!!!!!!!
OR GLaDOS in alpha stages?
It's improbable that it is GLaDOS because, as seen on the easter-egg in Portal 2, the borealis dissappeared from the dock in around the 60s or 70s (as that was the time of the chambers you were in were built) and, as we all know, GLaDOS is Caroline, but at the time the Borealis dissappeared Caroline was still alive, so if it was GLaDOS, it would be a very early version of just the empty shell before Caroline was put in as the AI. But, that would not be as valuable as the game makes it up to be, as GLaDOS is not physic, but she just controls Aperture Science as she is hooked up to it.