Zardnaar
Legend
With Morrus speculating about 5E Spelljammer I thought I would take a look at the various D&D settings and speculate how they could be done in 5E. Generally all of the settings could be done in 5E, some better than others- ye olde gritty Greyhawk or Darksun might not fit the core rules so will but you can tweak the core rules for a setting (varying the healing rate is easy).
The easiest settings.
Generally the easiest settings are the generic ones or ones close to it. Assuming you used other editions fluff these setting could easily be done in a book with say 3-5 settings in them and a poster map in the back. These are generally the sandbox settings with very few mechanical differences over the core rules. These are ones such as the Realms, Greyhawk, Nerath, Mystara and perhaps even Dragonlance and Eberron. You might want to have a list of allowed and banned races and classes, Greyhawk or Mystara for example might be a bit more restrictive than say Nerath or Eberron but that doesn't require a lot of page space. New things can be added for example moon magic in Dragonlance, Dragonmarks and Warforged in Eberron, Tortles and Rakasta for Mystara, Deva's and Warlords in Nerath but in the grand scheme of things you could probably give each setting 3-40 pages in a big book of settings type splat book assuming you of course ignored most of the fluff and let players do that via older material which is available on PDF. Planscape could also perhaps fit in here as the DMG also has planar rules and there are only a few mechanics you would need to update. A few key monsters iconic to the world could also fit in the book of worlds (Draconians etc). You could update these settings over 1-3 books with 2-5 settings per book. Ravenloft for example could share a book perhaps with another setting while Eberron/Mystara/Greyhawk/Nerath could probably fit in one book.
Settings That Need Additional Splatbook
This is mostly things like Darksun and perhaps Eberron if psionics are prominent. Both of these settings feature psionics. This splatbook ideally can be suitably generic however so you could use psionics on another world. The kickstarter Stronghold book could perhaps be another one if you wanted to do a ye olde Mystara/Greyhawk domain type game or perhaps even the Birthright setting. There is nothing stopping you using a domain type book on FR or Nerath but it was a bigger focus on other settings Mystara perhaps being the obvious one.
Settings That Probably Need their Own Book
These settings to somewhat faithfully adapt more or less require a full sized book devoted to them. This is because they drastically rewrite the rules from the core books or add lots of sub systems to enable the setting to achieve whatever it is meant to do. These are settings such as Darksun and Spelljammer. If you cut fluff out of other settings you can make them quite compact. This doesn't apply to these types of settings. A Spelljammer campaign for example kind of needs its own book and map for things like ship to ship combat and rules on D&D space. The 2E boxed set for example had 2 64 page books in it to be used on top of the PHB. Even condensed down in 5E you also need ship stats which will take up at least a chapter even with a few ships used- see star wars saga. A setting like Darksun kind of needs a lot of unique monsters, it rewrote the core rules (classes, races etc) and introduced new mechanics around exploring, spellcasting etc.
The Hardest Question?
TSR had a habit of metaplot heavy campaign settings. If you were to convert Dragonlance for example where on the timeline would you set it? For most of use I suppose the answer would be the War of the Lance but I am sure DL has its fans who would like it to pick up where it left off with Mina. There is no good answer here but generally I would base it on the original setting for several reasons. Those reasons are to introduce new players to a setting, less is more (you do not have to include later developments+ original ideas), and fans of later developments can usually easily advance the timeline themselves as long as you get the initial setting right. Unfortunately this may not be the best idea for Dragonlance since that has been done differently over 3 editions and another game system. Setting with frozen in time aspects get a big advantage here (Eberron, Nerath, Golarion?). No conversion of course is perfect but a 5E Spelljammer for example updating the 2E boxed set you can advance the timeline and add in the plots of the second Unhuman war if you want to and its very easy to do that.
The easiest settings.
Generally the easiest settings are the generic ones or ones close to it. Assuming you used other editions fluff these setting could easily be done in a book with say 3-5 settings in them and a poster map in the back. These are generally the sandbox settings with very few mechanical differences over the core rules. These are ones such as the Realms, Greyhawk, Nerath, Mystara and perhaps even Dragonlance and Eberron. You might want to have a list of allowed and banned races and classes, Greyhawk or Mystara for example might be a bit more restrictive than say Nerath or Eberron but that doesn't require a lot of page space. New things can be added for example moon magic in Dragonlance, Dragonmarks and Warforged in Eberron, Tortles and Rakasta for Mystara, Deva's and Warlords in Nerath but in the grand scheme of things you could probably give each setting 3-40 pages in a big book of settings type splat book assuming you of course ignored most of the fluff and let players do that via older material which is available on PDF. Planscape could also perhaps fit in here as the DMG also has planar rules and there are only a few mechanics you would need to update. A few key monsters iconic to the world could also fit in the book of worlds (Draconians etc). You could update these settings over 1-3 books with 2-5 settings per book. Ravenloft for example could share a book perhaps with another setting while Eberron/Mystara/Greyhawk/Nerath could probably fit in one book.
Settings That Need Additional Splatbook
This is mostly things like Darksun and perhaps Eberron if psionics are prominent. Both of these settings feature psionics. This splatbook ideally can be suitably generic however so you could use psionics on another world. The kickstarter Stronghold book could perhaps be another one if you wanted to do a ye olde Mystara/Greyhawk domain type game or perhaps even the Birthright setting. There is nothing stopping you using a domain type book on FR or Nerath but it was a bigger focus on other settings Mystara perhaps being the obvious one.
Settings That Probably Need their Own Book
These settings to somewhat faithfully adapt more or less require a full sized book devoted to them. This is because they drastically rewrite the rules from the core books or add lots of sub systems to enable the setting to achieve whatever it is meant to do. These are settings such as Darksun and Spelljammer. If you cut fluff out of other settings you can make them quite compact. This doesn't apply to these types of settings. A Spelljammer campaign for example kind of needs its own book and map for things like ship to ship combat and rules on D&D space. The 2E boxed set for example had 2 64 page books in it to be used on top of the PHB. Even condensed down in 5E you also need ship stats which will take up at least a chapter even with a few ships used- see star wars saga. A setting like Darksun kind of needs a lot of unique monsters, it rewrote the core rules (classes, races etc) and introduced new mechanics around exploring, spellcasting etc.
The Hardest Question?
TSR had a habit of metaplot heavy campaign settings. If you were to convert Dragonlance for example where on the timeline would you set it? For most of use I suppose the answer would be the War of the Lance but I am sure DL has its fans who would like it to pick up where it left off with Mina. There is no good answer here but generally I would base it on the original setting for several reasons. Those reasons are to introduce new players to a setting, less is more (you do not have to include later developments+ original ideas), and fans of later developments can usually easily advance the timeline themselves as long as you get the initial setting right. Unfortunately this may not be the best idea for Dragonlance since that has been done differently over 3 editions and another game system. Setting with frozen in time aspects get a big advantage here (Eberron, Nerath, Golarion?). No conversion of course is perfect but a 5E Spelljammer for example updating the 2E boxed set you can advance the timeline and add in the plots of the second Unhuman war if you want to and its very easy to do that.