Remember at the Schwartz's Walt mentioned facing East right before mentioning the name of the mountains, Sangre de Cristo. Well, the East has religious symbolism as all directions do. The East became a place where God intervened on behalf of his people, bringing them salvation. It's weird how he slipped in and out of places like a ghost, i.e. Skyler's pad. Perhaps it was a risen Walt returning to set matters straight. Intervening on behalf of his people (family, to include Jesse who was always family to him....in a very dysfunctional way). To turn the Red Door Black. Walt was the Anti-Christ.
Another poster had this theory which is related and along the same lines, although there are some holes in it, but nonetheless, food for thought. So many interpretations, so little time (2032).
He died in a New Hampshire bed in "Granite State" (IE, Rigor Mortis), and his last thoughts was the revenge fantasy that became "Felina". It's a reach, I know, but Granite = frozen, solid, unmovable: So "Granite State" could be interpreted as "frozen solid", hence rigor mortis. Plus: Marie is wearing white? Walt magically has his green shirt and khaki pants on when meeting Skyler? So many odd little details that don't quite make sense unless you see it as all playing out in Walt's mind. Again, it's a reach, but it somehow makes sense to me.