I speculate ...
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Each of these "wildspaces" is a setting that 5e is working on, and will be revealed in the future.
Realmsspace. The default setting is already revealed.
Eberron. Apparently, Eberron cannot be reached by the astral plane?
Athasspace. Athas of Dark Sun was revealed accidentally. It has a dark sun in the center of the system. Possibly even a black hole.
Doomspace. Alternate name for Athas. Athas is − nearly − impossible to access. However there was a difficult way to do it via the gray plane, which is now shadowfell in 5e. So the "doom" is this shadow route.
Wildspace (top). The "wildspace" at the top of the astral plane map has a planet (black circle) at its center. This is Oerth of Greyhawk. Like the ancient Ptolemaic cosmology, the sun and other planets revolve around the earth. The decentered sun is currently hidden off the edge of the image.
Astral Dominions are the outer planes, including farrealms and so on. Spelljammer = Planescape. Namely, Planejammer. That said. Spelljammer focuses on the astral sea. The lore that is in Mordenkainens Tomb of Foes and Volos will show up in a future Planescape product, possibly as part of Spelljammer dominions, or possibly as separate adventures.