This could be a completely separate campaign type. It begins with questing through the higher realms (somehow), and you ultimately decide which side to follow.
You’re sworn as either a Daedric Knight or Aedric Valkyrie.
It could be a Cyrodil-esque zone, but considerably harder NPC enemies that can join a battle randomly and wreak havoc. A new skill line opens to use some of the god’s powers while in the Ascendant Realms. They could have significantly long cool down times (to reflect the toll it takes on a mortal using the power of a god).
I’ll leave it just as a PvP notion. I had others to join it such as a new PvP trial (6 man teams - one representing each Aedra or Daedra - race to claim the trials prize. Some safeguards/bracketing relative to the difficulty and type of loot, so even lower levels can attempt to a novice effort. Blends PvP and PvE - PvE to reach the prize, but then a battle ensues. The prize team gets a solid buff, but the challengers can obtain the prize if they are able to defeat the superpowered prize claimants.
Thoughts?
DO. NOT. WIPE. (in game OR out!)