Hear me out. It's well documented that the player base hates Med'an, and most works Knaak, but simply continuing to ignore the character as if he doesn't exist, even though Blizzard has acknowledged him and his canon seems a bit short-sighted. Why not use him and put an end to him? Given Argus as a final boss was pulled out of left field to do nothing but establish the concept of World Souls, Med'an as the final boss of Legion possessed Sargeras would have both put an end to his character, while harkening back to his own father's fate. It would have also delivered on a final encounter with Sargeras that many fans feel robbed of.
It could have still happened as things did, and Argus could have still been a boss leading up to Med'an, just not the final one. We find out Sargeras has possessed Med'an (of course this would have required build up to the final patch with introducing Med'an earlier in the expansion's patch cycle), all leading up to a final showdown where we the players beat Sargeras out of him, killing Med'an, we find Sargeras in the cloud, and The Pantheon still banishes him as things happened in-game.
What do you think? Good idea, or would you have preferred what we got in the form of Argus?