Wizards of the Coast (WotC) uses code names for their development phase for products. “Marathon” was the official code name for  “Mordenkainen’s Tome of Foes“.

“Broadway” and “Catacomb” are the other released code names for the next products. “Broadway” should be announced in June as to what it will be. considering it’s marked HC & Dice (hardcover and dice), likely means another adventure module much like Tomb of Annihilation, which was “Dust” HC & Dice – which released with a hardcover, and a dice set…

Cloak = Curse of Strahd

Dagger = Storm King’s Thunder

Labyrinth = Tales from the Yawning Portal

Dust = Tomb of Annihilation

Midway = Xanathar’s Guide to Everything

Marathon = Mordenkainen’s Tome of Foes

“Broadway” WotC announcement in June!

NEW (2018/06/03): ‘Waterdeep: Dragon Heist’ adventure levels 1-5. Due out 2018 Sept. 18th

“Catacomb” expect an announcement likely in July or August.

NEW (2018/06/03): ‘Waterdeep: Dungeon of the Mad Mage’  adventure for levels 6-20. a 256-page adventure of Undermountain. Due out in 2018 Nov. 13th.

It’s very highly likely to be an adventure story-line hardcover.

Chris Perkins and Mike Mearls mentioned at the Gamehole 2017 panel that:

Potential for four major products for 2018 with a balance between rule crunch and adventures.

-Game Hole Con 2017, WotC hosted a “State of the Industry” panel, featuring Chris Perkins and Mike Mearls

They where in the play-testing phase of the book. There’s guesses of it being a city campaign –

D&D “Broadway” HC

By Rpg Team Wizards
ISBN: 9780786966257
format: Hardcover
series: D&D Adventure
pages: 256
publisher: Wizards of the Coast
pub. date: 2018-09-18

D&D “Broadway” Dice

By Rpg Team Wizards
ISBN: 9780786966288
format: Game
series: D&D Accessory
pages: n/a
publisher: Wizards of the Coast
pub. date: 2018-09-18

D&D “Catacomb” HC

By Rpg Team Wizards
ISBN: 9780786966264
format: Hardcover
series: D&D Adventure
pages: 256
publisher: Wizards of the Coast
pub. date: 2018-11-20

Current guesses are that “Catacomb” maybe a city adventure – perhaps Waterdeep, with Undermountain? But I hold hope for Sigil, the City of Doors – which would be awesome!

End of 2018

There’s another book scheduled for the end of 2018 – but no information. Guesses are either the first Setting book, or a compilation of other adventures similar to “Tales from the Yawning Portal” – perhaps centered around the Rage of Demons story arcs.

Settings

At the earliest we can expect more Multiverse settings in 2018, but more likely in 2019.

One challenge D&D had in the 90s was the settings were competing with each other. But now that they are thinking of settings as a “genre” as opposed to a “place” it twists a bit what they can do with a setting, so it does not necessarily have to compete anymore.

Genre becomes the focus, as a means of changing what the feel of D&D will be for a game, and as a means of explaining that setting to a new player.

-Game Hole Con 2017, WotC hosted a “State of the Industry” panel, featuring Chris Perkins and Mike Mearls

“Gothic-Horror D&D”  is Ravenloft (released in 2016)

“Post-Apocalyptic D&D” being Dark Sun – which is waiting for a strong Psionics system for 5e.

“Film-Noir D&D” or “Pulp D&D”  likely Eberron

They have an idea of what they want to do with Eberron, but a lot of it just comes down to doing it right, so they take the time to make sure that when it comes out it will feel like a definitive book.

-Game Hole Con 2017, WotC hosted a “State of the Industry” panel, featuring Chris Perkins and Mike Mearls

Planescape 

They have a rough draft cosmological ties for how all the settings could come back and fit together … They want to make sure for each setting product, they assume this is the first time you’re seeing that setting, and not require prior knowledge of it.

-Game Hole Con 2017, WotC hosted a “State of the Industry” panel, featuring Chris Perkins and Mike Mearls

Unfortunately I will have to agree with some online mentions in that Planescape maybe released in 1-2 years after at least one other setting, or after the “genre settings” have mostly been released (Dark Sun, Eberron).

They had also previously confirmed a project board for SpellJammer.

My hope is that the D&D team release a new book for Psionics in early 2019, followed closely by Darksun setting.