I think it's worth noting that everyone's ignoring Gamma World in this thread as well. Which is a fair thing to do as GW was marketed as a "Separate Product" through it's history, but was really a heavy reskin of D&D. Gamma World is alongside Forgotten Realms and Dragonlance as having been present through D&D's history since 1st edition.
So I suspect that the three settings are:
1. Dragonlance - Been at least as successful as a product line as Forgotten Realms over the years, the only D&D product to have heavy penetration outside of the RPG market so it has a lot of recognition and power to bring in new customers, well known brand in many circles, highly marketable in movies and TV, dedicated built-in large audience to evangelize, very large novel range with the potential to bring in even more sales in E-Books increasing profitability, deeply invested writers who've asked WOTC to give them access. Dragonlance is a lock as one of the three settings.
2. Gamma World - Been released adjacent to pretty much every edition of D&D, been reasonably successful, has the ability to introduce a sci-fi aspect to D&D that allows for variety and breaks up monotony, post-apocalyptic material is still a hot seller right now.
3. Planescape - Dedicated fanbase, rules for very high level play supporting groups who've been playing for some time and want to advance higher, introduces a "Hub" to allow DMs to bring in different worlds.
Why I think the rest are out:
1. Al-Qadim - They didn't just go slapping warning labels all over their old product to bring back a setting certain to cause more outrage.
2. Kara-Tur - As above. There's no way they're doing this.
3. Dark Sun - About as popular as Gamma World and Planescape, but doesn't bring anything to the table beyond it. Planescape is high level and a hub, Gamma World is a different experience with familiar rules, Dark Sun is just a setting with nothing else going for it.
4. Greyhawk - In the same boat as Dark Sun, plus it's largely been on a shelf for decades so it just doesn't have a wide draw.
5. Birthright - Wasn't popular when it was in publication, it has no draw to it any more.
6. Spelljammer - Fills the same niche as Planescape, but doesn't open doors to different places as easily, and doesn't bring the high level play support. Not really a reason to pick it over Planescape.
7. Other settings - The other one-off or two-off settings tried over the years definitely aren't going to sell.
I'm going to have to disagree about Dragonlance being a lock. And it is for the same reason TSR never was able to sustain it much after 1st edition. Once the novels by Weis and Hickman came out and shot into the stratosphere they quickly eclipsed everything else. Witness how many people here seem to think the setting was created by Tracy Hickman and Margaret Weis.
It wasn't.
The initial concept was dreamed up by Tracy and Laura Hickman, and then Douglas Niles, Harold Johnson, Larry Elmore, Jeff Easley and a whole lot of other TSR staffers that most have forgotten. Weis was an editor who was given the job of getting someone to adapt the modules into novels and then when she couldn't find a suitable author, did it her self. She was not an RPG designer but succeeded as a novelist beyond what anyone would have envisioned at the start of the project. (And Hickman himself rapidly transitioned to novelist more than designer)
Whereas the Forgotten Realms was a setting with a novel line, Dragonlance became a novel line with the occasional RPG book. Dark Sun can be revived in 4th edition and ignore the novels because no one cared about the Dark Sun novels. Notice even Forgotten Realms has never "undone" their novel canon, in the end, they catapulted the timeline forward and then ended their novel line. And the Realms novels are far less central to the setting than Dragonlance's is.
The modules theoretically can be played without the Heroes of the Lance, and without following the plot of the novels, but as the novels gained popularity and became the main entry point to Dragonlance I would say the groups that would actually do that became rarer and rarer. For most, players and readers alike, the novels
were Dragonlance.
So the designers from 2nd edition onwards were faced with a conundrum: How do I keep Dragonlance as a setting for play, rather than novels. There were some great attempts - Taladas at first, setting the RPG material on a different continent than the novels, theoretically solving the problem. But for most Dragonlance = Ansalon and nothing would come in the way of that,no matter how imaginative or creative Zeb Cook's creation was. So the Tales of the Lance boxed set was released along with other products mostly set after the War of the Lance. But still, they couldn't compete with the novels. So they just gave up and released 2nd edition conversions of the original modules, complete with the stats of the Heroes of the Lance.
Weis and Hickman then effectively "blew up" the world, at the time meant to be a final end to their contributions. But some imaginative designers were able to salvage a new setting out of it, which TSR used to showcase an innovative new system. But because it wasn't AD&D it wasn't embraced (despite having probably some of the best fluff ever, and a fantastic bestiary), fans were divided on the changes to the setting. Wizards of the Coast, the new owners, ended the experiment, while Weis and Hickman were brought back to write the "War of Souls", the "Sundering" of Dragonlance, ending with a setting that had the best of the old and new. With the novels winding down there was more freedom for the RPG to reclaim it and the 3rd edition Dragonlance team (including Cam Banks) did some excellent sourcebook allowing play in all time periods, in a cohesive world that acknowledged the novels but allowed players to step out of their shadow.
So now more than a decade later we look at how can this setting be revived? I know what my preference is - a setting book allowing play in all eras that acknowledges the novels but doesn't seek to try and retell them. However I might be an outlier, since everyone seems to want a "reimagining" of the original modules. (Isn't that effectively a slightly bigger scope Tyranny of Dragons). But to most people that won't be Dragonlance, since Autumn Twilight and its siblings loom far too large in the collective imagination. So I imagine we could get yet another conversion of the original modules. I'm sure that will please many, but to me that would be another missed opportunity.
