D&D 5E Let's put together a list of what is supposedly in the DMG.

[Evenglare]

From what I have heard so far.... please post any I missed so I can update the list.

Variant Rules/Modules:

MP system
Variant HP / lasting wound rules
Using Proficiency dice
Mass combat
Going past level 20
A more indepth skill system(s?)
Chases
THAC0
Downtime Rules
Domain Management

General DMG/extra rules:

Creating the feel of older editions
Magic Items
Magic Item Creation
Monster Creation
Traps
Trap Creation
General World Building/Adventure Building Rules
Wilderness/Dungeon Exploration Rules
Class Building Guidelines
Evil class material: Blackguard / Oathbreaker Paladin, Death Domain for Clerics,
Race Building Guidelines
Warforged Race
Kender Race
Planar Cosmology
Firearms
Ship/Vehicle
Possibly different genres

 

[Li Shenron]

Well obviously Magic Items themselves

Also you forgot the "evil" material, e.g. Blackguard subclass and Death domain.

Dungeon/Wilderness Exploration rules (the more detailed one in the playtest, not the ones in Basic), unless they fit in the PHB.

Mearls also mentioned chase rules at some point.

edit: not sure if you count this as part of Mass battle rules, but the DMG is also supposed to have rules for running large groups of monsters at once (mob rules?)

 

[fjw70]

Guidance on modifying the game to replicate the style of earlier editions. Including a THACO sidebar.

Aspect-like skill system (similar to Fate).

 

[Thaumaturge]

Guidelines for creating the feel of each edition.

Thaumaturge.

Edit: Way of Shadow'd

 

[MarkB]

Planar cosmology.

 

[Gundark]

I really hope that the Mass Battles stuff allows for epic armies clashing and not just "warband" type of stuff.

 

[Remathilis]

Planar cosmology.

That is going to be touched on in the PHB, but there may be more in the DMG.

 

[AverageCitizen]

Aspect-like skill system (similar to Fate).

Really? I really liked Fate's aspects.

 

[Boarstorm]

More downtime rules.

 

[the Jester]

Domain management rules.