I think that D&D needs to return to the crazy literary, mythic, and non-specific gestalt cosmology pre-3rd Ed. There would not be a core or default campaign setting at all, and no core pantheon of gods. The various categories of gods would be outlined and referred to, the Astral Gods, Elemental Primordials, Archfey (need a better name for them) and other similar beings of cosmic power. Perhaps a chart in the Player's Handbook (or Red Box) that lists sample deities with just enough information to tie them mechanically to clerics.
Beyond the Red Box and core three rulebooks, supplements such as the Manual of the Planes and Deities and Demigods would describe the D&D cosmology and reference the classic crazy mish-mash of gods. Tell me where the Olympians hang out, where the Aesir and Vanir battle for eternity, where the various deities of the Realms claim turf. I'd like to see a return to the "meta-setting" of D&D, where the various campaign worlds all exist in the same multiverse, perhaps even interacting in the Astral Sea, the Elemental Chaos, or even in Shadow or Faerie.
Yeah.