A single gods astral domain, or would a place somewhere in the Feywild be a better fit?
Im no artist but I think it would look something like this:Of course Abeir shouldnt be considered its own plane, it only intersects with Toril, not all of Realmspace, at least as far as I know, I should just erase it, im not sure how to best show the position of Abeir on a 2 dimensional planar map, but it proably has a connection to the Plane of Dreams and the Plane of Nightmares as well.
Maybe Gray will come along with a great explanation.
That does look good Silver...
The 4e cosmology doesn't use the Ethereal Plane, although, the cosmology is supposed to be the same as the 3e cosmology with changes wrought by the Spellplague. So the question is, what happened to the Ethereal Plane? My assumption is that it was merged with the Shadow Plane (or the part of the Shadow Plane that was coterminous with Toril) to become the Shadowfell. In that case the Plane of Dreams might now be a region of the Shadowfell that separates the border of Shadow from Deep Shadow.
Alternatively, you could postulate that the Ethereal was absorbed into the Feywild. The Region of Dreams might then have become part of the Feywild.
Or, it is possible that the Ethereal was split half and half between the two. Here's a thought: the Plane of Dreams might have been itself split. Perhaps the Region of Dreams exists in the Feywild while a dark reflection, the Region of Nightmares, exists in the Shadowfell. There is precedence for a Demiplane of Nightmares, though last I heard, I believe that plane was a demiplane attached to the Astral.
Which brings us to another option, which is to have the Plane of Dreams be a demiplane attached to the Astral. Not a divine dominion, but a demiplane in its own right. And there is a logic to that, the Astral Plane is a plane of mind and thought. Dreams would be at home there.
A final option is to simply not place it at all. Why does anyone need to know where it is? You simply access it through your dreams or by means of other rituals. It's ultimate location with respect to the rest of the cosmology need not be known to the players, nor even resolved in the DM's mind as it is unlikely to be important to the plot of the adventure--important merely that players be able to get there. Its location makes for a good mystery, with different plausible theories espoused by different sages, some debating it heatedly. You don't really need to decide on its location unless some plot point relies on fixing it definitively.
My guess is that when the gods and primordials settled their war and split Abeir off from Toril, the primordials got tricked, they forgot to ask for a sun. So as a result they ended up with a planet in a dark pocket universe with no sun. What they did for a sun in the meantime is a story yet to be told, however, at some point an incredibly vast Dawn Titan named Arambar died (he may have been killed or alternatively may have sacrificed himself) and the residual energy formed the Steelsky.
I like the idea that he sacrificed himself shortly after Abeir was created in order to light the darkness. But we don't know that his death was contempraneous (or willing) with the creation of Abeir. It is possible that they used other means to light the sky at first, maybe salamanders lit up the sky with fire, maybe they constructed giant lamps, maybe a giant primordial rowed around the sky in a great boat with some kind of light source. They might even have tried a few different solutions in succession. All we know is that the Steelsky seems to be the current method.
It would therefore seems likely that when the Spellplague stirred up the Elemental Planes and mixed them all into the Elemental Chaos, the Ethereal Plane collapsed and got stirred into the mix. One might therefore conclude that the Plane of Dreams also got sucked into that maelstrom and would find its present home in the Elemental Chaos, existing as a ribbon of colors threaded through certain parts of the plane. Or alternatively, the Veil of Dream might itself have collapsed, like the surface of a bubble, and find itself concentrated in a particular region of the Chaos, might even be hard to find--laying hidden among the detritus of elemental motes, somewhere deep within the elemental miasma.
Come to think of it, actually locating the Plane of Dreams and traveling there might make the basis for a very fun adventure in itself.
I guess we'll have to wait for the next PH to reveal how dream, elemental and shadow spells and their planar sources interact.
Addendum: I forgot.
I saw that Dendar the Nightserpent resides in the Fugue Plane. Did he always live there or did he hail from the Plane of Nightmares? If so, this might be evidence that the plane of dreams merged with the Fugue somehow.
She has always lived on the Fugue Plane, except in 2e, the Fugue Plane was thought to be located in the Gray Waste of Hades. In 3e the Fugue Plane was determined to be a plane in its own right.
Dendar was born of the first nightmare ever dreamed by a mortal in Realmspace. But, aside from this, as far as I know, Dendar has no links to the Plane of Nightmares, although in Calimport she is known (incorrectly) as the Mother of the Night Parade. (see Powers & Pantheons p. 188)
I think it would make sense for a plane of dreams to overlap Realmspace, Abeir, Feywild, and the Shadowfell. Where it touched with the Feywild you have good dreams, where it touches with the Shadowfell is Nightmares. Just a thought, and I dont really think theres a wrong or right answer.
I still think the planes are pretty much as they were before, other than the Abyss getting booted out of the Outerplanes, or by 4e terminology the Astral sea. The way I see it, The planes are far more vast and complex than mortal minds can understand. So the way mortals choose to map these planes and how they interact may change, but for the most part its still the same planes.