Sargeras at a time possessed Medivh and by extension is the Lord of the ravens. If this is true wouldn't "The lord of the ravens will turn the key" be pointing towards Sargeras stabbing azeroth before his imprisonment?
To add on to that, wouldn't the "Five keys to open our way. Five torches to light our path" line be a reference to us using the pillars to open the way to (indirectly) Argus which would in turn set the Lord of the ravens business in motion along with ushering in the 3rd death of Azeroth (Sargeras stabbing it)