This article shows a series of objects sent mysteriously to PC Gamer and their conclusions of them. They are just guesses but some pretty good ones, I think.
And thus I reached the conclusion that the box of mystery indicates such: A Rift expansion is coming and it will bring a 10-level increase in the level cap, two new raids, four new souls, six new areas, a new city called Port Tempest, and possibly something fancy to use those Inert Prisms for. If I’m right, we should have more details to share with you soon.
New souls and a level cap increase? Fog, you have anything you could add?