On this blog some new information has been found out:
Forgotten Realms 4e is three books, period, done, end of line: Forgotten Realms Campaign Guide, Player’s Guide to FR, and DM’s Guide to FR. All settings will be done like that, one per year, until they run out of settings. They mentioned Greyhawk, Ravenloft, Dark Sun, and Spelljammer as settings on their list! Eberron, of course, is the ‘09 setting release (same three books), but it will also get DDI updates starting in June.
For example, the Products Page lists no "Forgotten Realms GMs Guide" and we've already been told that the Campaign Setting is for DM's.
It would be redundant to make the Campaign Setting DM-primary, then release another book for DM's.
As for that being the end of the line for a campaign, we can only speculate until we hear from WotC directly, but with FR and Eberron there's *so much* content to explore that it seems WotC would be shooting themselves in the foot to not release more books.
Regions of those settings have room to be fleshed out. As do assorted factions and/or races.
Is it possible they'll have a "three and done" policy on Campaigns? Sure. Is it likely? I'd say no.
That was a limited setting. At the outset, the designers had a 2 year schedule as to what books they wanted to produce and then they would end the line.
Fan demand (and sales) gave it one more year but that was it. I always thought because of this Al-qadim has the highest quality per sourcebook of any of the TSR 2E settings produced.
It would be redundant to make the Campaign Setting DM-primary, then release another book for DM's.
I'm guessing the Campaign Setting will be maps, area info, monsters, etc., The DM guide will be encounter charts, NPCs, etc, and the player's guide classes, feats, and so on.
PHB
- setting specific classes and races (aka, artificer and warforged in eberron)
- description of the major powers and geography
- specific history of setting and mythology
-etc
DMG
- setting specific encounters
- DM information on NPCs, including stats for setting specific ones
- setting specific magic items
- etc..
MM
- setting specific monsters and creatures
three core books, all you need to run the game in that setting. Mind you, I can see WOTC or it's 3rd party partners producing adventures set within that setting as well, but no need for other core books.. makes sense?
I applaud this new format! Campaign Settings that don't take up more shelf space than the core game! Plus it sounds like each campaign setting might be going limited print runs / once per year so they won't have multiple campaign settings releasing at the same time and competing. Under this model, I could see myself getting each 4E updated setting as it came out. And I'm delighted to see 4E Greyhawk might be on the horizon.
Another thing to consider, with Dragon and Dungeon being in-house, is having supplemental articles supporting a setting beyond the three books printed in the online mags...
If they come out with Spelljammer in 4 or 5 years then I guess they'll get my money then. 
1. For those uninterested in FR or Eberron but attracted to Spelljammer or Dark Sun, all the Eberron & FR releases mean little, so it makes more sense to release different settings rather than focus on but a few.
2. Because playing in a setting may mean one has to keep up with it, containing it to a few releases works against intimidating new players (DMs markedly).
3. Just because you have one setting doesn't restrict your buying of another, and groups may like switching between or among sets for thematic breaks (I do).
Perhaps we'll see a new East Asian culture setting!
Hear hear!
I'm all for a Spelljammer update! I;m also really looking forward to a Dark Sun revival!
On a side note, I like this format much better. I would rather buy smatterings of a few varied settings than dozens of FR or Eberron books.
Someone was asking about this...resently?
I really hope to see PlaneScape, Ravenloft, and Spelljammer make a comeback.
And I know a guy who will forgive everything WotC has ever done that ticked him off if they release a 4th ed Darksun that's a decent treatment.
Course, Darksun will have to wait until after the Core PHB that deals with Psionics.
Btw, are you the Crashbeedo from the Mystara boards a few years back?
Dark Sun was one of the best departures from standard D&D that they ever released. I love the distinct flavor of the Dark Sun world, from the Dragon to the Giants of the Sand Sea, to the immersion in Psionics.
And who doesn't love feral halflings?
I would like to see a 4E Dark Sun and Spelljammer most of all, both of those were very interesting and I'd like to see if 4E's up to the challenge of doing these great old settings.
I'd also be curious to see them do a take on Jakandor. It had some very, very interesting takes on D&D, but the 2E ruleset just wasn't able to hold up to the wonderful backdrop that was created.
I have my doubts of a 4E Ravenloft being decent; S&S did a decent job but I don't care for EtCR and Heroes of Horror at all.
I like Heroes of Horror, but I don't feel it was as effective a tool as the old 2E Ravenloft boxed set. I think 4E could effectively treat the Demiplanes, but, as always, it's dependent on the hard work that the development teams put in.
Any setting can be adapted to a rules set, it just depends on the treatment it gets.
"Return to Castle Ravenloft" in 3E was STELLAR.
Body ---------------------- Type
Helios/Sun ---------- Fire
Hermes/Mercury ----- Earth
Aphrodite/Venus ----- Earth
Gaea/Earth ---------- Earth
Selene/Moon -------- Earth
Ares/Mars ----------- Earth
Asteroid Belt -------- Earth
Zeus/Jupiter -------- Air
Chronos/Saturn ----- Air
Uranos/Uranus ------ Water
Poseidon/Neptune --- Water
Pluton/Pluto --------- Ice
Helios is a ball of fire about the same size as our Sun, since this is a magical universe, it is a magical fire and fire elementals live there.
Hermes is a baked rock, largely rocky desert, it nevertheless has a breathable atmosphere. The Sun looms large on this world, there are two oasises on this planet, one at the North Pole and one at the South, it is inhabited largely by heat loving creatures, lots of red dragons, fire newts, salamanders. Much of the activity occurs below the surface of this world
Aphrodite is covered with a perpetual cloud layer which obscures its surface, the climate is wet hot and humid, and is inhabited by dinosaurs, primitive humans, lizardmen, much of the flat terrain is swamp if not ocean volcanoes and earthquakes are fairly common on this world.
Gaea is this system's version of Earth, the continents and geographic features are the same as on our own Earth, history however has taken a different turn. The history of this world begins in 323 B.C.E., before this time its history is identical to our world, but in the year 323 B.C.E. a mysterious happening called simply the Event marked a great influx of magic or monsters into this world, for reasons that aren't clear the laws of physics changed, but whatever the reason Alexander the great did not die in 323 B.C.E. as in our history, instead he lived on to about 280 B.C.E., and this gave him time to build up his empire, called the Alexanderian Empire, by most historians, this empire lasted until about what would have been 300 A.D. in our dating system, but because of this radical departure in history, the three great monotheistic religions never developed, there is no Islam, or Christianity, and the Kingdom of Israel was absorbed by the Alexandrian Empire and assimilated. The D&D gods replaced the various superstitions that existed at the time and developed into a universal pantheon by about 1000 A.D., when the Vikings brought the new religion over to the Americas, the fact that priests of these new gods could cast spells while the old ones didn't certainly helped.
Ares is a magical version of planetary romance Mars, there was an ancient civilization which dug canals to irrigate the entire planet with meltwaters from the polar ice caps, this civilization fell and Ares is now a tangle of competing city states along these canals, much of the canal system is in disrepair with some canals having gone dry when they silted up and on the banks of these canals are ruined or abandoned cities - a source of much treasure and adventure to the intrepid.
Asteroid Belt this is an archipelago of various rock islands in space, following the rules of spelljammer, many of these have breathable atmospheres and have vegitation and inhabitants. These serve as ports of call for many a spelljammer ship.
Zeus is an air planet, the atmosphere is breathable, and there are various floating islands high in its atmosphere with multicolored banded clouds.
Chronos is similar to Zeus, but is has a large prominent ring system which serves as a hiding place for space pirates and the "scum and villany" of wildspace.
Uranos and Poseidon are water planets, they have breathable atmospheres surrounding planets that are all water, one can sail on the ocean surface endlessly without encountering any land because there isn't any, plenty of sea monsters and sea creatures though, mercreatures and various "fish-people" also inhabit this place.
Pluton is simply a ball of ice, lots of white dragons and other cold loving creatures live here. There are a few other frozen bodies including comets out here before reaching the crystal sphere Pluton has three moons by the way, one large moon called Charon and two other smaller moons.
"Return to Castle Ravenloft" in 3E was STELLAR.
Not in my opinion - EtCR was an atrocious abomination and corruption of the original. Playable by itself, but when set against all the old Ravenloft stuff, it was garbage.
I know its scope is a limited now, because of the redesign of the multiverse, but I think there was enough substance to the campaign world for it to exist in its own right.