-- HOW TO GET THE EXPANSION PACK --

[AnttiApina]

From the blog:

Now with the Portal 2 ARG over, we will release the new content, an add-on story called "Justine", for all non-steam versions of the game aswell. And there might be other surprises too

Looks like there is something else coming up.

I myself cannot wait to play the expansion since I saw a short video at GameTrailers. I haven't watched a video since. I still have to wait for my copy of Portal 2 so this will be a fine way to spend time.