If D&D fandom cared, we'd already have such a system.
Having seen a lot of editions come and go, and seen a lot of fandom discussions, it's pretty much the case that many (probably most) fans just praise whatever's the status quo.
I mean, if, at the beginning of 5E (or any other time in WotC/TSR history) the desingers had fully implemented a Marvel/DC/Transformers style in-world designation for continuity, many people (maybe you yourself, though I can't speak for you), would be like: "This is great!" Or at least, it would've been just accepted.
And, if on this forum, I'd argued the opposite: that WotC should just fuzzily handwave the difference between various Timelines and Realities, many of the same people would be like: "If D&D fandom wanted fuzzily handwaved Timelines and Realities, we'd already have such a fuzzily handwaved system."
Back in 4E, a huge percentage of people (including on ENWorld) were like: 4E is the best ever; if fandom cared for a different system, we'd already have such a system. Same for 3E. Same for 2E. Same for 1E, etc. A very large percentage of people just assume whatever the way it is now must be the best it could ever be (except for a few complaints here or there, edition wars and such).
It's cumbersome and unnecessary, and doesn't really play into the genre or the game as played.
Obviously we disagree here. It's all a matter of degree. There's probably someone even further on the spectrum of 'fuzzily handwaved continuity' than you. They could be like: "I want all D&D adventures to be standalone stories which are not tied to each other at all, and which are set in no campaign setting. I don't want campaign settings to advance their timelines. In fact, no campaign settings at all!" And so forth. I'm all for that sandbox, utilitarian approach, as long as the storied worlds are recognized as alternate timelines, and are supported in other ways.
The comic book houses of DC and Marvel have labeled their many alternate worlds, because they all exist simultaneously (well, until destroyed in a Crisis), and characters travel between them in the stories. There was a great scene in the Flash TV show, when the characters were first trying to wrap their heads around alternate universes . . . they started numbering them to keep track.
In D&D stories, you might have planar adventurers traveling between the various planes of existence . . . but rarely does anybody tell stories about traveling between continuities. Especially as the differences are so minor, and really just represent canon shifts and not alternate realities within the world of the game.
That's a good point, and you encapsulate an important difference between comic book companies and an RPG company.
But we do already have glimpses and fragments of such a meta-continuity system, even in D&D. Here are examples from D&D products which involve the co-existence of multiple continuities, rather than just planar travel:
- The system from Appendix I in AD&D 1e Manual of the Planes, which gives numerical designations describing Alternate Prime Material Planes, based on three factors: Physical Factor (PF), Magical Factor (MF), and Temporal Factor (TF).
- Gygax's continuum of alternate Oerths, based on their degree of magic-vs.-technology: Oerth, Yarth, Aerth, Uerth, and Earth.
- The world of Uerth (an evil mirror of Oerth) in 3E Expedition to the Ruins of Castle Greyhawk.
- "Up, Away, and Beyond" DRAGON mag article by Bruce Heard, which explains the co-existence of rules-based realities, which can be crossed over using a new deity-level spell "Reality Shift." The article explains how Immortals from the BD&D "game universe" (what I call Multiverse-B), such as Odin, co-exist as deities in Multiverse-1.
- The Alternate World Gates from AC4: The Book of Marvellous Magic, where a Bard from Multiverse-1 crosses over to Multiverse-B, and mutters something about "incompatibility." Not to mention crossovers with various Earth timelines (Boot Hill, Gangbusters, Dawn Patrol) and Sci-Fi settings (Gamma World and Star Frontiers).
- 2E Chronomancy sourcebook.
- The different continuities of the The River of Time in the Dragonlance setting. They exist in-world, and some characters know of their co-existence. Of all the D&D settings, DL probably has the most prominent concept of "alternate timelines", since these actually play into the novels and fiction. There was a whole 3E DL sourcebook devoted to alternate timelines.
- Bruce Cordell's terminology in his Die Vecna Die! 2E-to-3E conversion adventure (in the paragraphs which explain how Multiverse-2 is metamorphosing into Multiverse 3) and his Alternity Tangents sourcebook, both of which refer to "superspace." Also the reference to "half-worlds" and "paraverses." That one word "superspace", confirms that the D&D Multiverse is shared with Alternity's Tangent cosmology. The Tangents sourcebook is the most "clearly complex" system for Parallel Planes ever published by TSR. It has a numerical designation for each Parallel Plane, based on an X-Y axis. There are five divisions of superspace: Historical, Biological, Cosmological, Fantastic, and Beyond.
- The Alternity Tangents system was distilled for d20 Modern as the Dimension X campaign model in d20 Future. And the similar Project Javelin campaign model which was released as free PDF.
- Back when WotC had the Star Wars RPG license, there's was one (and only one!) official cross-over adventure seed between all the d20Modern Alternate Dimensions, the D&D Multiverse, and the Star Wars Universe! See d20 Modern Project Javelin Campaign Primer, p.4: "For the purpose of the Project Javelin adventures, the alternate dimensions are the mini-settings found in the various d20 MODERN books. GMs wishing to create some filler adventures to complete the progression from level 1 to 20 are encouraged to either use the settings from those books or create new and different worlds. For example, one farflung dimension might resemble the standard DUNGEONS & DRAGONS multiverse, and another the STAR WARS universe."
So such as system has existed in piecemeal, its just that it hasn't yet been brought to full clarity and fruition.
Transformers . . . that's a special case. The hardcore fans are nuts! And I say that as a Transformers fan. There are a lot of reboot/reimaginings of the Transformers franchise, and super-fans are of course keeping track. However, does Hasbro care about any of that? (I honestly don't know the answer to that question, but I'm going to guess it's "no").
Hasbro cared enough to support the Vector Prime series of Official articles which laid out the Universal Stream meta-system. It's not just "super-fan(atic)s" spinning out fan-fic schemes. I'm not saying its as big a concern as the next Transformers blockbuster, but WotC cared enough to publish "super-fan" Brian James' complied FR timeline. Which I well remember as just a "fan webpage" before WotC tapped him and turned it into a proper hardcover book. On his website, he did the other worlds' timelines too: Temporal Chronology of the Primes. Anyway, Hasbro and WotC and TSR cared enough to present these meta-systems, even if, in D&D's case, it hasn't come to fruition currently.
There are not distinct D&D continuities between editions, the canon has evolved over the decades, mostly being additive, with minor changes . . . with the slight exception of 4th Edition's left turn.
Minor changes?
Time of Troubles? Changed Toril-1 into Toril-2.
Fate of Istus? Changed Oerth-1 into Oerth-2.
Chaos War? Changed Krynn-1 into Krynn-S.
Wrath of the Immortals? Changed Mystara-B3 into Mystara-B4. (BECMI > Rules Cyclopedia)
Die, Vecna, Die!? Changed Multiverse-2 into Multiverse-3.
The Apocalypse Stone? Sample for changing any world from Multiverse-2 to Multiverse-3.
War of Souls? Changed Krynn-S into Krynn-3.
Spellplague? Changed Toril-3 to Toril-4 and Abeir. Also changed entire Multiverse-3 into Multiverse-4.
Second Sundering? Changed Toril-4 to Toril-5. Also changed rest of Multiverse-4 into Multiverse-5.
I'm not worried that WotC will do anything like you are proposing, I certainly hope they don't!
Yes, for goodness sakes, don't worry!
But there is nothing stopping interested fans like yourself from doing so . . . just don't expect to get any sort of large-scale interest from the rest of the fanbase on your classification scheme.
Nice wittle eggheaded super-fans can play by demselves in de corner. haha
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