Thanks guachi and Chaosmancer for sharing about your campaign worlds. Yep, your version of the D&D Multiverse consists of just one world, along with those few extraplanar places you mentioned.
In contrast, the published D&D Multiverse has always consisted of a number of different D&D Worlds, and there have always been cross-overs between *all* of them, even back in the 1970s and 1980s. Oerth existed alongside its parallel Earths: Yarth, Aerth, and Uerth. Murlynd visited Earth, where he got his six-shooters. The original Greyhawk campaign also visited Lewis Carrol's Wonderland and Edgar Rice Burrough's Barsoom (Mars). The Mystara Gazetteers included appendices which detailed gates between Mystara, Oerth, and Toril. The Book of Marvellous Magic had Alternate World Gates which brought characters to and from Mystara, Oerth, Boot Hill, Gamma World, Star Frontiers, Dawn Patrol, and Gangbusters. Ed Greenwood had "real world" Egyptians and Mesopotamians journey from Earth to Toril. One of Mystara's most (in)famous NPC families (the Ambrevilles) came from Earth (aka Laterre). The 1e Dragonlance hardcover had rules for bringing characters from other D&D worlds. The Wizards Three (Elminster, Dalamar, and Mordenkainen) from three different D&D worlds, visited each other in Wisconsin. As you surely know, there were hundreds of Planescape, Ravenloft, and Spelljammer products (along with Chronomancer) which featured all sorts of storied connections between D&D Worlds. There were whole novels written about characters who adventured from one world to the next. Even in 3E, which differentiated each world with a distinct planar cosmology--all the worlds were still connected via the Plane of Shadow, which also connected with the d20 Modern settings such as Urban Arcana. 4E explicitly made events, such as the Dawn War, occur in all the published worlds. The 5E PHB and DMG are the first to explicitly list all of the classic D&D worlds. WotC reps have repeatedly said that all the D&D worlds still exist in 5E, and that all the worlds reside in the same Multiverse (as they have in every edition), and that they'll "all" be re-visited in 5E, eventually.
These connections already exist. Every edition of D&D has portrayed the D&D Multiverse as consisting of multiple campaign worlds which can be visited at the DM's discretion. It's not like Crawford is sitting down inventing connections out of the blue. He's just restating that 44-year-long interconnectedness in 5E terms.
Furthermore, Magic: The Gathering, like D&D, is also based on a Multiverse of multiple worlds...and Magic fans don't complain...they're not overwhelmed by the connections. And now we're finding out that the M:TG worlds exist in the D&D Multiverse, as a sort of greater "WotC Multiverse." That is a new connection, but it's still only an expansion of the existing multiplicity of the D&D Multiverse.
Guachi and Chaosmancer, I respect that you're both DMs whose discretion is to stick to one world, and that's that. Cool. Yet I'd prefer you refrain from so grumpily misrepresenting what the published D&D Multiverse has been all along: interconnected.
I think you may have misinterpretted what I was getting at, maybe if I break some of my thoughts down further it will help.
In response to your thoughts on my campaign world, you are correct, I don't care
if the worlds are connected. One way or the other, does not matter to my games. I've already got seven or more planes of existence to juggle, doubling or tripling them by connecting whole other worlds does not appeal to me.
However, I think a larger part of the discussion and my personal thoughts goes to the second point. I don't care
how they are connected. And that is the entire premise of settings like Planescape and Spelljammer. They seek to explain exactly how (From your list of examples) Murlynd visited Earth. They give reliable ways for any person who has the knowledge to go from Plane of Existence A to Plane of Existence B. And that's great if that is what you are into, but I find it completely unnecessary. If I wanted throw Superman, Legacy (Paulina Parsons), and Atlas into Waterdeep to fight The Cult of the Dragon... I'd just do it. I don't need to explain how those points all intersect. And it creates a series of problems when you try and spell it out.
Take Star Trek as an example, the people on a given planet may have a certain perception of reality, such as space is full of ghosts and the stars are the gods who watch over them. However, they are fundamentally wrong about that reality, and the reasons the crew of the Enterprise doesn't come down and correct them is because doing so violates the right of those civilizations to learn about the truth for themselves. However, it breeds a sense of superiority doesn't it? Anyone visiting that planet from space knows that these people have no idea what is actually going on, and therefore they are somewhat lessened in comparison.
We have that already. We have the idea that planescape scholars scoff at people stuck in one plane, because they don't know the "real story". And we can scoff at them, because the planescape people don't realize they are all characters in our made up stories to entertain ourselves (multiverse theories being what they are, all multiverses are connected with all other multiverses, and an infinite array of potential truths).
But we don't need any of it. We don't need to explain how it is all connected and what is all looks like when you zoom all the way out. We can just as easily (as [MENTION=6803664]ccs[/MENTION] points out) just use the planeshift spell, or a macguffin, and get the result of going from point A to point B.
That's the bigger thing for me personally, these settings answer questions I don't need answers to. Other people want them and other people find the neccessary to their enjoyment of the game. Great, go nuts, but I don't need flying ships through explosive magic stuff between galaxy sized crystals that are grains of sand to explain how some guy one time went from Oerth to Earth and shook hands with Stan Lee. The characters aren't going to meet Stan Lee in my game, because it would detract from the story I am telling at the time. And someone telling me that despite my dislike they are already connected anyways.... doesn't matter. I don't care how long they've been connected, how many times they've been connected, or how important it is they are connected. It is never going to come up, my players aren't interested.