To be metaphorically precise, Nurgle is Entropy. Which is why he's simultaneously about both life/change and eventual annihilation in the heat-death-of-the-universe sense.
But yeah, this is the rumour thread so rumours: Seems like Malign Portents is either going to focus on Nurgle vs Death or else they're at least tying in all the released together. On the other hand we know the incoming Black Library books focus on "soul wars" which suggests a conflict with Order, since that's Nagash's whole beef with Sigmar, that he's supposedly 'poaching' souls due to Nagash to make Stormcasts.