Lanefan
Victoria Rules
OK, I'll play.Okay maybe not traps
- Players Handbook
- Species
- Classes
- Feats
- Necessary Core Spells (Fireball, Magic Missile, Read Magic, Hunter's Mark)
- Dungeon Monsters Guide
- Traps
- Planes and Environments
- Hazards
- Bastions
- "Necessary" Core Magic Items (+1 sword, Flame tongue, Dragon Scale Armor)
- Monster Manual
- Monsters
- Humaniods NPC statblocks
- Monster Spells
- Tome of Magic
- Bulk of Spells
- Bulk of Magic Items
- Psionics
- Runes
- Infusions
- Anime Fightin' Magic Attacks
This way a DM does not technically have to buy four books. Old core spells that a DM or Players needs are in the PHB.
But if you want those legacy spells like Aganazzar's Scorcher or book fillers like Flame Arrows or theme spells like "Acid spell #4", you buy the magic book.

Players' Handbook
--- Species
--- Classes
--- --- Spells (they are, after all, class abilities; the bulk of 'em should be here)
--- --- Pantheons and Deities (Clerics need these in order to function)
--- Feats, Skills, Backgrounds (whichever of those still exist in 6e)
--- Roll-Up Guide (step by step)
--- Equipment Guide
--- How to Play
--- --- Combat Rules (player-side)
--- Example of Play (a la 1e DMG page 97-ish)
DMG
--- Traps and Hazards
--- Planes, Worlds, and Environments (brief overview)
--- Magic Item Prices and Write-ups (yes, all of 'em)
--- Combat Rules (DM-side)
--- Game Management (time, recordkeeping, playstyles discussion, etc.)
--- Options and Dials (to make the game harder, easier, or otherwise different than the default)
--- Short-Form Char-gen (easy NPC construction while still keeping them 100% compatible and comparable with PCs)
--- Downtime Guide
--- --- Bastions and Strongholds
--- --- Spell Research and Item Creation rules
--- --- Training to Level
Monster Manual
--- Monsters, Monsters, and more Monsters (but NO rewrites of PC species as those are already in the PH)
--- --- Monster Abilities, listed under the relevant monster
--- More Monsters
Expansions Book (target audience: DMs)
--- Worldbuilding Guide
--- --- Planes, Worlds, and Environments (deeper dive)
--- Optional Spells
--- Optional Classes (psionics go here)
--- Conversion Guides (to 6e from each other edition)
--- High-Level Play options and suggestions
--- More Options and Dials
Notice anything missing there? That's right, there's no "encounter-building" piece in the DMG. That's intentional; as such things have never really been great in any edition, a simple few paragraphs explaining some basics and encouraging some trial and error is all this needs - and all it'll get.