1. An actually detailed cosmological/galactic/phlogistonic map of the D&D Multiverse, showing the location of each and every previously mentioned planet, moon, plane, demiplane, dimension, alternate timeline, and reality, from all editions of D&D, and all TSR/WotC rpg lines (Alternity, d20 Modern, etc). Something like the most detailed Star Wars Galaxy map.
2. Include a full-page planetary map of each of the major worlds (Abeir-Toril, Ravenloft, Oerth, Athas, Krynn, Eberron, Mystara, Aebrynis, Nerath, "D&D Earth" (Urban Arcana/Historical Reference), Sigil, and Rock of Bral), with an icon showing where every published adventure is officially placed or suggested. (Several sites exist in more than one world - e.g. Keep on the Borderland.)
3. Include Chronomancy so that, not only all the worlds can be visited, but also, all the times (e.g. Arcane Age of FR, Age of Blackmoor of Mystara, Age of Istar in Dragonlance). Include a timeline of the D&D Multiverse, lining up all the chronologies of the various worlds (and taking into account the mathematics of how some worlds have shorter years!). Also make space for sidestream timelines for continuity snags and alternate/parallel storylines, such as the various d20 Modern Campaign Models set on Earth.
4. Make reference to Bruce Heard's
"reality" concept, so as to make clear the distinction between the Original Reality, Classic Reality, Advanced Reality, Second Reality, Saga Reality, Third Reality, Fourth Reality, and Fifth Reality. There are eight main Realities of the D&D Multiverse.
5. Introduce a slight connection with the rest of the
Hasbro Universe via a wider "Megaverse" beyond the D&D Multiverse proper: Dominaria (M:tG), Transformers, Go-Bots, GI Joe, Action Man, Equestria, Micronauts, M.A.S.K., Jem and the Holograms, Clue, Visionaries, and ROM: Space Knight. So that these can become D&D settings in the future, and leverage the upcoming Hasbro Cinematic Universe films.