Storm of Chaos and Eye of Terror weren't retconed they were erased because nothing of concequence actually happened in them. The results were inconclusive and a little dull (other than Grimgor smacking Archaon around but not killing him) pretty much status quo ante bellum . Medusa V did give rise to an increase in the Tau Empire and a codex of the same name. Dark Shadows added some funky magic items to the better performing races and let's not forget Ichar IV which is now well ingrained in Ultramarine Lore.
I'd agree this one has much more scope although I wouldn't expect Archaon, Sigmar or Nagash to buy it or indeed Sigmaron to burn. Still it'll looks like fun and as others have pointed out the background in AoS is still in its infancy so there's plenty of room to forge a narative with a Global campaign